 8. My Dear Sir, having attempted in my last letter to explain to you the simple and admirable office subserved by the oxygen of the atmosphere in its combination with carbon in the animal body, I will now proceed to present you with some remarks upon those materials which sustain its mechanisms in motion and keep up their various functions, namely the elements. If the increase in mass in an animal body, the development and reproduction of its organs depend upon the blood, then those substances only which are capable of being converted into blood can be properly regarded as nourishment. In order then to ascertain what parts of our food are nutritious, we must compare the composition of the blood with the composition of the various articles taken as food. Two substances require a special consideration as the chief ingredients of the blood, one of these separates immediately from the blood when it is withdrawn from the circulation. It is well known that in this case blood coagulates, and separates into a yellowish liquid, the serum of the blood, and a gelatinous mass which adheres to a rod or stick in soft elastic fibers when coagulating blood is briskly stirred. This is the fibrin of the blood which is identical in all its properties with muscular fiber when the latter is purified from all foreign matters. The second principle ingredient of the blood is contained in the serum and gives to this liquid all the properties of the white of egg with which it is indeed identical. When heated it coagulates into a white elastic mass and the coagulating substance is called albumin. Fibrin and albumin, the chief ingredients of blood, contain in all seven chemical elements among which nitrogen, phosphorus, and sulfur are found. They contain also the earth of bones. The serum retains in solution sea salt and other salts of potash and soda in which the acids are carbonic, phosphoric, and sulfuric acids. The globules of the blood contain fibrin and albumin along with a red coloring matter in which iron is a constant element. Besides these the blood contains certain fatty bodies in small quantity which differ from ordinary fats in several of their properties. All analysis has led to the remarkable result that fibrin and albumin contain the same organic elements united in the same proportion, i.e. that they are isomeric, their chemical composition, the proportion of their ultimate elements being identical. But the difference of their external properties shows that the particles of which they are composed are arranged in a different order. This conclusion has lately been beautifully confirmed by a distinguished physiologist, Dennis, who has succeeded in converting fibrin into albumin, i.e. in giving it the solubility and coagulability by heat which characterized the white of egg. Fibrin and albumin, besides having the same composition, agree also in this, that both dissolve in concentrated muriatic acid, yielding a solution of an intense purple color. This solution, whether made with fibrin or albumin, has the very same reactions with all substances yet tried. Both albumin and fibrin in the process of nutrition are capable of being converted into muscular fiber and muscular fiber is capable of being reconverted into blood. These facts have long been established by physiologists and chemistry has merely proved that these metamorphoses can be accomplished under the influence of a certain force. Without the aid of a third substance or of its elements and without the addition of any foreign element or the separation of any element previously present in these substances. If we now compare the composition of all organized parts without a fibrin and albumin, the following relations present themselves. All parts of the animal body which have a decided shape, which form parts of organs, contain nitrogen. No part of an organ which possesses motion and life is destitute of nitrogen. All of them contain likewise carbon and the elements of water, the latter however, in no case in the proportion to form water. The chief ingredients of the blood contain nearly 17 percent of nitrogen and from numerous analyses it appears that no part of an organ contains less than 17 percent of nitrogen. The most convincing experiments and observations have proved that the animal body is absolutely incapable of producing an elementary body such as carbon or nitrogen out of substances which do not contain it and it obviously follows that all kinds of food fit for the production either of blood or of cellular tissue, membranes, skin, hair, muscular fiber, etc must contain a certain amount of nitrogen because that element is essential to the composition of the above named organs because the organs cannot create it from the other elements presented to them and finally because no nitrogen is absorbed from the atmosphere in the vital process. The substance of the brain and nerves contains a large quantity of albumin and in addition to this two peculiar fatty acids distinguished from other fats by containing phosphorus, phosphoric acid, one of these contains nitrogen, fremi. Finally water and common fat are those ingredients of the body which are destitute of nitrogen. Both are amorphous or unorganized and only so far take part in the vital process as that their presence is required for the due performance of the vital functions. The inorganic constituents of the body are iron, lime, magnesia, common salt, and the alkalis. The nutritive process is seen in its simplest form in carnivorous animals. This class of animals lives on the blood and flesh of the gruminophora but this blood and flesh are in all their properties identical with their own. Neither chemical nor physiological differences can be discovered. The nutriment of carnivorous animals is derived originally from blood. In their stomach it becomes dissolved and capable of reaching all other parts of the body. In its passage it is again converted into blood and from this blood are reproduced all those parts of their organization which have undergone change or metamorphosis. With the exception of hooves, hair, feathers, and the earth of bones every part of the food of carnivorous animals is capable of assimilation. In a chemical sense therefore it may be said that a carnivorous animal in supporting the vital process consumes itself. That which serves for its nutrition is identical with those parts of its organization which are to be renewed. The process of nutrition in gruminophorous animals appears at first sight altogether different. Their digestive organs are less simple and their food consists of vegetables. The great mass of which contains but little nitrogen. From what substances it may be asked is the blood formed by means of which their organs are developed. This question may be answered with certainty. Chemical researchers have shown that all such parts of vegetables as can afford nutriment to animals contain certain constituents which are rich in nitrogen and the most ordinary experience proves that animals require for their support and nutrition less of these parts of plants in proportion as they abound in the nitrogenized constituents. Animals cannot be fed on matters destitute of these nitrogenized constituents. These important products of vegetation are especially abundant in the seeds of the different kinds of grain and of peas, beans, and lentils in the roots and the juices of what are commonly called vegetables. They exist however in all plants without exception and in every part of plants in larger or smaller quantity. These nitrogenized forms of nutriment in the vegetable kingdom may be reduced to three substances which are easily distinguished by their external characters. Two of them are soluble in water. The third is insoluble. When the newly expressed juices of vegetables are allowed to stand a separation takes place in a few minutes. A gelatinous precipitate commonly of a green tinge is deposited and this when acted on by liquids which remove the coloring matter leaves a grayish-white substance well known to druggists as the deposit from vegetable juices. This is one of the nitrogenized compounds which serves for the nutrition of animals and has been named vegetable fibrin. The juice of grapes is especially rich in this constituent but it is most abundant in the seeds of wheat and of the cerealia generally. It may be obtained from wheat flour by a mechanical operation and in a state of tolerable purity. It is then called gluten but the glutinous property belongs not to vegetable fibrin but to a foreign substance present in small quantity which is not found in the other cerealia. The method by which it is obtained sufficiently proves that it is insoluble in water although we cannot doubt that it was originally dissolved in the vegetable juice from which it afterwards separated exactly as fibrin does from blood. The second nitrogenized compound remains dissolved in the juice after the separation of the fibrin. It does not separate from the juice at the ordinary temperature but is instantly coagulated when the liquid containing it is heated to the boiling point. When the clarified juice of nutritious vegetables such as cauliflower, asparagus, mangle whirsel, or turnips is made to boil a coagulum is formed which it is absolutely impossible to distinguish from the substance which separates as a coagulum when the serum of blood or the white of an egg diluted with water are heated to the boiling point. This is vegetable albumin. It is found in the greatest abundance in certain seeds in nuts, almonds, and others in which the starch of the griminier is replaced by oil. The third nitrogenized constituent of the vegetable food of animals is vegetable casein. It is chiefly found in the seeds of peas, beans, lentils, and similar leguminous seeds. Like vegetable albumin it is soluble in water but differs from it in this that its solution is not coagulated by heat. When the solution is heated or evaporated a skin forms on its surface and the addition of an acid causes a coagulum just as an animal milk. These three nitrogenized compounds vegetable fiber albumin and casein are the true nitrogenized constituents of the food of griminophores animals. All other nitrogenized compounds occurring in plants are either rejected by animals as in the case of the characteristic principles of poisonous and medicinal plants or else they occur in the food in such very small proportion that they cannot possibly contribute to the increase of mass in the animal body. The chemical analysis of these three substances has led to the very interesting result that they contain the same organic elements united in the same proportion by weight and what is still more remarkable that they are identical in composition with the chief constituents of blood, animal fibrin, and albumin. They all three dissolve in concentrated muriatic acid with the same deep purple color and even in their physical characters animal fibrin and albumin are in no respect different from vegetable fibrin and albumin. It is especially to be noticed that by the phrase identity of composition we do not here intend mere similarity but that even in regard to the presence and relative amount of sulfur, phosphorus, and phosphate of lime no difference can be observed. How beautifully and admirably simple with the aid of these discoveries appears the process of nutrition in animals the formation of their organs in which vitality chiefly resides. Those vegetable principles which in animals are used to form blood contain the chief constituents of blood fibrin and albumin ready formed as far as regards their composition. All plants besides contain a certain quantity of iron which reappears in the coloring matter of the blood. Vegetable fibrin and animal fibrin vegetable albumin and animal albumin hardly differ even in form. If these principles be wanting in the food the nutrition of the animal is arrested and when they are present the grimoire forest animal obtains in its foods the very same principles on the presence of which the nutrition of the carnivore entirely depends. Vegetables produce in their organism the blood of all animals for the carnivore in consuming the blood and flesh of the grimoire consume strictly speaking only the vegetable principles which have served for the nutrition of the latter. Vegetable fibrin and albumin take the form in the stomach of the grimoire forest animal as animal fibrin and albumin do in that of the carnivorous animal. From what has been said it follows that the development of the animal organism and its growth are dependent on the reception of certain principles identical with the chief constituents of blood. In this sense we may say that the animal organism gives to the blood only its form that it is incapable of creating blood out of other substances which do not already contain the chief constituents of that fluid. We cannot indeed maintain that the animal organism has no power to form other compounds for we know that it is capable of producing an extensive series of compounds differing in composition from the chief constituents of blood but these last which form the starting point of the series it cannot produce. The animal organism is a higher kind of vegetable the development of which begins with those substances with the production of which the life of an ordinary vegetable ends. As soon as the latter has born seed it dies or a period of its life comes to a termination. In that endless series of compounds which begins with carbonic acid ammonia and water the sources of the nutrition of vegetables and includes the most complex constituents of the animal brain there is no blank no interruption. The first substance capable of affording nutriment to animals is the last product of the creative energy of vegetables. The substance of cellular tissue and of membranes of the brain and nerves these the vegetable cannot produce. The seemingly miraculous in the production agency of vegetables disappears in a great degree when we reflect that the production of the constituents of blood cannot appear more surprising than the occurrence of the fat of beef and mutton and cocoa beans of human fat in olive oil of the principal ingredient of butter in palm oil and of horse fat and train oil in certain oily seeds. End of letter eight. Section nine of familiar letters on chemistry this is a LibriVox recording all LibriVox recordings are in the public domain for more information or to volunteer please visit LibriVox.org recording by ML Cohen Cleveland Ohio March 2007 familiar letters on chemistry letter nine my dear sir the facts detailed on my last letter will satisfy you as to the manner in which the increase of mass in an animal that is its growth is accomplished we still have to consider a most important question namely the function performed in the animal system by substances destitute of nitrogen such as sugar starch gum pectin etc the most extensive class of animals the gramma nivora cannot live without these substances their food must contain a certain amount of one or more of them and if these compounds are not supplied death quickly ensues this important inquiry extends also to the constituents of the food of carnivorous animals in the earliest periods of life for this food also contains substances which are not necessary for their support in the adult state the nutrition of the young of carnivora is obviously accomplished by means similar to those by which the gramma nivora are nourished their development is dependent on the supply of a fluid which the body of the mother secretes in the shape of milk milk contains only one nitrogenized constituent known under the name of casing besides this its chief ingredients are butter parentheses fat and prins and sugar of milk the blood of the young animal its muscular fiber cellular tissue nervous matter and bones must have derived their origin from the nitrogenized constituent of milk the casing for butter and sugar of milk contain no nitrogen now the analysis of casing has led to the result which after the details i've given can hardly excite your surprise that this substance also is identical in composition with the chief constituents of blood fibrin and albumin nay more a comparison of its properties with those of vegetable casing as shown that these two substances are identical in all their properties in so much that certain plants such as peas beans and lentils are capable of producing the same substance which is formed from the blood of the mother and employed in yielding the blood of the young animal the young animal therefore receives in the form of casing which is distinguished from fibrin and albumin by its greater solubility and by not coagulating when heated the chief constituent of the mother's blood to convert casing into blood no foreign substance is required and in the conversion of the mother's blood into casing no elements of the constituents of blood have been separated when chemically examined casing is found to contain a much larger proportion of the earth of bones than blood does and that in a very soluble form capable of reaching every part of the body thus even in the earliest period of its life the development of the organs in which vitality resides is in the carnivorous animal dependent on the supply of a substance identical in organic composition with the chief constituents of its blood what then is the use of the butter and the sugar of milk how does it happen that these substances are indispensable to life butter and sugar of milk contain no fixed bases no soda nor potash sugar of milk has a composition closely lied to that of the other kinds of sugar of starch and of gum all of them contain carbon and the elements of water the latter precisely in the proportion to form water there is added therefore by means of these compounds to nitrogenize constituents of food a certain amount of carbon or as in the case of butter of carbon and hydrogen that is an excess of elements which cannot possibly be employed in the production of blood because the nitrogenized substances contained in the food already contain exactly the amount of carbon which is required for the production of fibrin and albumin in the adult carnivorous animal which neither gains nor loses weight perceptively from day to day its nourishment the waste of organized tissue and its consumption of oxygen stand to each other in a well-defined and fixed relation the carbon of the carbonic acid given off without of the urine the nitrogen of the urine and the hydrogen given off as ammonia and water these elements taken together must be exactly equal in the weight to the carbon nitrogen and hydrogen of the metamorphose tissues and since these last are exactly replaced by food to carbon nitrogen and hydrogen of the food where there's not the case the weight of the animal could not possibly remain unchanged but in the young of the carnivorous the weight does not remain unchanged on the contrary it increased from day to day by an appreciable quantity this fact presupposes that the assimilative processes in the young animal is more energetic more intense than the process of transformation in the existing tissues if both processes were equally active the weight of the body could not increase and where the waste by transformation greater the weight of the body would decrease now the circulation of the young animal is not weaker but on the contrary more rapid the respirations are more frequent and for equal bulks the consumption of oxygen must be greater rather than smaller in the young than in the adult animal but since the metamorphosis of organized parts goes on more slowly there would ensue a deficiency of those substances the carbon and hydrogen which are adapted for a combination with oxygen because in the carnivora nature has destined the new compounds produced by the metamorphosis of organized parts to furnish the necessary resistance to the action of the oxygen and to produce animal heat what is wanting for these purposes an infinite wisdom has supplied to the young in its natural food the carbon and hydrogen of butter and the carbon of sugar of the milk no part of either of which can yield blood fiber and albumin are destined for the support of the respiratory processes at an age when a greater resistance is opposed to the metamorphosis of existing organisms or in other words that a production of compounds which in the adult state are produced in quantity amply sufficient for the purpose of respiration the young animal receives the constituents of its blood in the casing of the milk a metamorphosis of existing organs goes on for bile and urine are secreted the materials of the metamorphose parts are given off in the form of urine of carbonic acid and of water but the butter and sugar of milk also disappear they cannot be detected in the feces the butter and sugar of milk are given out in the form of carbonic acid and water and their conversion into oxidized products furnishes the clearest proof that far more oxygen is absorbed than is required to convert the carbon and hydrogen of the metamorphose tissues into carbonic acid and water the change in metamorphosis of organized tissues going on in the vital processes in the young animal consequently yield in a given time much less carbon and hydrogen in the form adapted for the respiratory processes then correspond to the oxygen taken up in the lungs the substance and if its organized parts would undergo a more rapid consumption and would necessarily yield to the action of the oxygen or not the deficiency of carbon and hydrogen supplied from another source the continued increase of mass or growth and the free and unimpeded development of the organs of the young animal are dependent on the presence of foreign substances which in a nutritive process have no other function than to protect newly formed organs from the action of the oxygen the elements of these substances unite with the oxygen the organs themselves could not do so without being consumed that is growth or increase of mass in the body the consumption of oxygen remaining the same would be utterly impossible the preceding considerations leave no doubt as to the purpose for which nature has added to the food of the young of carnivorous mammalia substance devoid of nitrogen which their organism cannot employ for nutrition strictly so-called that is for the production of blood substances which may be entirely dispensed with in the nourishment in the adult state in the young of carnivorous birds the one of all motion is an obvious cause of diminished waste in the organized parts hence milk is not provided for them the nutritive processes in the carnivore thus presents itself under two distinct forms one of which we meet again in the gramonivora in the gramonivorous animals we observe that during their whole life their existence depends on the supply of substances having a composition identical with that of sugar of milk or closely resembling it everything that they consume as food contains a certain quantity of starch gum or sugar mixed with other matters the function performed in the vital processes of the gramonivora by these substances is indicated in a very clear and convincing manner when we take into consideration the very small relative amount of the carbon which these animals consume in the nitrogenized constituents of their food which bears no proportion whatever to the oxygen absorbed through the skin and lungs a horse for example can be kept in perfectly good condition if he obtains his food 15 pounds of hay and four and a half pounds of oats daily if we now calculate the whole amount of nitrogen in these matters as ascertained by analysis parentheses one and one-half percent in the hay 2.2 percent in the oats and parentheses in the form of blood that is as fibrin and albumin with the due proportion of water in the blood parentheses 80 percent the horse receives daily no more than four and a half ounces of nitrogen corresponding to about eight pounds of blood but along with this nitrogen that is combined with it in the form of fibrin and albumin the animal receives only about 14 and a half ounces of carbon without going further into the calculation it will readily be admitted that the volume of air inspired and expired by a horse the quantity of oxygen consumed and as a necessary consequence the amount of carbonic acid given out by the animal are much greater than in the respiratory process in man but an adult man consumed daily about 14 ounces of carbon and the determination of bosn galt according to which a hourist expires 79 ounces daily cannot be very far from the truth in the nitrogenized constituents of food therefore the horse receives rather less than the fifth part of the carbon which his organism requires for the support of the respiratory process and we see that the wisdom of the creator has added to his food the four fists which are wanting in various forms as starch sugar etc with which the animal must be supplied or his organism will be destroyed by the action of the oxygen it is obvious that in the system of the gram anivara whose food contains so small a portion relatively of the constituents of the blood the process of metamorphosis and existing tissues and consequently the restoration or reproduction must go on far less rapidly than in the carnivora or this not the case of vegetation a thousand times more luxuriant than the actual one would not suffice for the nourishment sugar gum and starch would no longer be necessary to support life in these animals because in that case the products of the waste or metamorphosis of the organized tissues would contain enough carbon to support the respiratory process end of section nine recorded by ml co and cleveland ohio march 2007 section 10 of familiar letters on chemistry this is a liber box recording all liber box recordings are in the public domain for more information or to volunteer please visit liberbox.org recording by ml co and cleveland ohio march 2007 familiar letters on chemistry by justice lee big letter 10 my dear sir let me now apply the principles announced in the preceding letters to the circumstances of our own species man when confined to animal food requires for his support and nourishment extensive sources of food even more widely extended than the lion and tiger because when he has the opportunity he kills without eating a nation of hunters on the limited space is utterly incapable of increasing his numbers beyond a certain point which is soon attained the carbon necessary for respiration must be obtained from the animals of which only a limited number can live on the space supposed these animals collect from plants the constituents of their organs and of their blood and yield them in turn to the savages who live by the chase alone they again receive this food unaccompanied by those compounds destitute of nitrogen which during the life of the animals serve to support the respiratory process in such men confined to an animal diet it is the carbon of the flesh and of the blood which must take the place of starch and sugar but 15 pounds of flesh contains no more carbon than four pounds of starch and while the savage with one animal and an equal weight of starch should maintain life and health for a certain number of days he would be compelled if confined to flesh alone in order to procure the carbon necessary for respiration during the same time to consume five such animals it is easy to see from these considerations how close the connection is between agriculture and the multiplication of the human species the cultivation of our crops is ultimately no other object than the production of a maximum of those substances which are adapted for assimilation and respiration in the smallest possible space grain and other nutritious vegetables yield us not only in starch sugar and gum the carbon which protects our organs from the action of oxygen and produces in the organism the heat which is essential to life but also in the form of vegetable fibrin albumin and casing our blood from which the other parts of our body are developed man when confined to animal food respires like the carnivore at the expense of the matters produced by the metamorphosis of organized tissues and just like the lion tiger hyena in the cases of a menagerie are compelled to accelerate the waste of the organized tissues by incessant motion in order to furnish the matter necessary for respiration so the savage for the very same object is forced to make the most laborious exertions and go through a vast amount of muscular exercise he is compelled to consume force merely in order to supply matter for respiration cultivation is the economy of force science teaches us the simplest means of obtaining the greatest effort with the smallest expenditure of power and with given means to produce a maximum of force the unprofitable exertion of power the waste of force in agriculture in other branches of industry in science or in social economy is characteristic of the savage state or of the want of knowledge in accordance with what i have already stated you will perceive that the substances of which the food of man is composed may be divided into two classes into nitrogenized and non-nitrogenized the former are capable of conversion into blood the latter are incapable of this transformation out of those substances which are adapted to the formation of blood are formed all the organized tissues the other class of substances in the normal state of health serve to support the process of respiration the former may be called the plastic elements of nutrition the latter elements of respiration among the former we reckon vegetable fibrin vegetable alpumin vegetable casing animal flesh animal blood among the elements of respiration in our food are fat pectin starch baserine gum wine cane sugar beer grape sugar spirits sugar of milk the most recent and exact researches have established as a universal fact to which nothing yet known is opposed that nitrogenized constituents of vegetable food have a composition identical with that of the constituents of the blood no nitrogenized compound the composition of which differs from that of fibrin albumin and casein is capable of supporting the vital process in animals the animal organism unquestionably possesses the power of forming from the constituents of its blood the substances of its membranes and cellular tissue of the nerves and brain and of the organic part of cartilage and bones but the blood must be supplied to it perfect in everything but its form that is in its chemical composition if this be not done a period is rapidly put to the formation of blood and consequently to life this consideration enables us easily to explain how it happens that the tissues yielding gelatin or chondrine as for example the gelatin of skin or of bones are not adapted for the support of the vital process for their composition is different from that of fibrin or albumin it is obvious that this means nothing more than that those parts of the animal organism which form the blood not possess the power of affecting a transformation in the arrangement of the elements of gelatin or of those tissues which contain it the gelatinous tissues the gelatin of the bones the membranes the cells of the skin suffer in the animal body under the influence of oxygen and moisture a progressive alteration a part of these tissues is separated and must be restored from the blood but this alteration and restoration are obviously confined within very narrow limits while in the body of a starving or sick individual the fat disappears and the muscular tissue takes once more the form of blood we find that the tendons and membranes retain their natural condition and the limbs of the dead body their connections which depend on the gelatinous tissues on the other hand we see that the gelatin of bones devoured by a dog entirely disappears while only the bone earth is found in his excrement the same is true of man when fed on food rich in gelatin as for example strong soup the gelatin is not to be found either in the urine or in the feces and consequently must have undergone a change and must have served some purpose in the animal economy it is clear that the gelatin must be expelled from the body in a form different from that in which it was introduced as food when we consider the transformation of the albumen of the blood into a part of an organ composed of fibrin the identity and composition of the two substances renders the change easily conceivable indeed we find the change of dissolved substance in an insoluble organ of vitality chemically speaking natural and easily explained on account of this very identity of composition hence the opinion is not unworthy of closer investigation the gelatin when taken in the dissolved state is again converted in the body into cellular tissue membrane and cartilage that it may serve for reproduction of such parts of these tissues as have been wasted and for their growth and when the powers of nutrition in the whole body are affected by a change of the health then even should the power of forming blood remain the same the organic force by which the constituents of the blood are transformed into cellular tissue and membranes must necessarily be enfeebled by sickness in the sick man the intensity of the vital force is powered to produce metamorphosis must be diminished as well in the stomach as in all other parts of the body in this condition the uniform experience of practical physician shows that gelatinous matters in a dissolved state exercise the most decided influence on the state of the health given in the form adapted for assimilation they served the husband the vital force just as may be done in the case of the stomach by due preparation of the food in general brittleness in the bones of gram-eniverse animals is clearly owing to a weakness in those parts of the organism whose function it is to convert the constituents of the blood into cellular tissue and membrane and if we can trust to the reports of the physicians who have resided in the east the turkish women and their diet of rice and the frequent use of enamada of strong soup have united the conditions necessary for the formation both of cellular tissue and of fat end of section 10 recording by ml cohen cleveland ohio march 2007 section 11 of familiar letters on chemistry this is a libra vox recording all libra vox recordings are in the public domain for more information or to volunteer please visit libra vox.org recording by lorisa jewarski brisbane australia march 2007 familiar letters on chemistry by justice leebig letter 11 my dear sir in the immense yet limited expense of the ocean the animal and vegetable kingdoms are mutually dependent upon and successive to each other the animals obtain their constituent elements from the plants and restore them to the water in their original form when they are again serve as nourishment to a new generation of plants the oxygen which marine animals withdraw in their respiration from the air dissolved in seawater which is returned to the water by the vital processes of sea plants that air is richer in oxygen than atmospheric air containing 32 to 33 percent oxygen also combines with the products of the putrification of dead animal bodies changes their carbon into carbonic acid their hydrogen into water and the nitrogen assumes again the form of ammonia thus we observe in the ocean a circulation takes place without the additional subtraction of any element unlimited in duration although limited in extent in as much as in a confined space the nourishment of plants exists in a limited quantity we well know that marine plants cannot derive a supply of humus for their nourishment through their roots look at the great seetang the fucous gigantius this plant according to cook reaches a height of 360 feet and a single specimen with its immense ramifications nourishes thousands of marine animals yet its root is a small body no larger than a fist what nourishment can this draw from a naked rock upon the surface of which there is no perceptible change it is quite obvious that these plants require only a hold a fastening to prevent a change of place as a counterpoise to their specific gravity which is less than that of the medium in which they float that medium provides necessary nourishment and presents it to the surface of every part of the plant seawater contains not only carbonic acid and ammonia but the alkaline and earthy phosphates and carbonates required by these plants for their growth and which we always find as a constant constituents of their ashes all experience demonstrates that the conditions of the existence of marine plants are the same which are essential to terrestrial plants but the latter do not live like sea plants in a medium which contains all their elements and surrounds with appropriate nourishment every part of their organs on the contrary they require two media one of which namely the soil contains those elements which are absent from the medium surrounding them i.e the atmosphere is it possible that we could ever be in doubt respecting the office which the soil and its component parts serve in the existence and growth of vegetables that there should have been a time when the mineral elements of plants were not regarded as absolutely essential to their vitality has not the same circulation been observed on the surface of the earth which we have just contemplated in the ocean the same incessant change disturbance and restitution of equilibrium experience in agriculture shows that the production of vegetables on a given surface increases with the supply of certain matters originally parts of the soil which had been taken up from it by plants the instruments of man and animals these are nothing more than matters derived from vegetable food which in the vital process of animals or after their death assumes again the form under which they originally existed as parts of the soil now we know that the atmosphere contains none of their substances and therefore can replace none and we know that their removal from a soil destroys its fertility which may be restored and increased by a new supply it is possible after so many decisive investigations into the origin of the elements of animals and vegetables to the use of alkalis of lime and the phosphates any doubt can exist as to the principles upon which a rational agriculture depends can the art of agriculture be based upon anything but the restitution of a disturbed equilibrium can it be imagined that any country however rich and fertile with a flourishing commerce which for centuries exports its produce in the shape of grain and cattle will maintain its fertility if the same commerce does not restore in some form of manure those elements which have been removed from the soil and which cannot be replaced by the atmosphere must not the same fate await every such country which has actually befallen the once prolific soil of virginia now in many parts no longer able to grow its former staple productions wheat and tobacco in the large towns of england the produce both of english and foreign agriculture is largely consumed elements of the soil indispensable to plants do not return to the fields contrivances resulting from the manners and custom of the english people and peculiar to them render it difficult perhaps impossible to collect the enormous quantity of phosphates which are daily as solid and liquid excrements carried into the rivers these phosphates although present in the soil in the smallest quantity are its most important mineral constituents it was observed that many english fields exhausted in that manner immediately doubled their produce as if by miracle when dressed with bone earth imported from the continent but if the export of bones from germany is continued to the extent it has hitherto reached our soil must be gradually exhausted and the extent of our loss may be estimated by considering that one pound of bones contains as much phosphoric acid as a hundred weight of grain the imperfect knowledge of nature and the properties and relations of matter possessed by the alchemists gave rise in their time to an opinion that metals as well as plants could be produced from a seed the regular forms and ramifications seen in crystals they imagined to be the leaves and branches of metal plants and as they saw the seeds of plants grow producing root stem and leaves and again blossoms fruit and seed apparently without receiving any supply of appropriate material they deemed it worthy of zealous inquiry to discover the seed of gold and the earth necessary for its development if the metal seeds were once obtained might not they entertain hopes of their growth such ideas could only be entertained when nothing was known of the atmosphere and its participation with the earth in administering to the vital processes of plants and animals modern chemistry indeed produces the elements of water and combining them forms water anew but it does not create those elements it derives them from water the new form to artificial water has been water before many of our farmers are like the alchemists of old they are searching for the miraculous seed the means which without any further supply of nourishment to a soil scarcely rich enough to be sprinkled with indigenous plants shall produce crops of grain a hundred fold the experience of centuries nay thousands of years is insufficient to guard men against these fallacies our only security from these and similar absurdities must be derived from a correct knowledge of scientific principles in the first period of natural philosophy organic life was supposed to be derived from water only afterwards it was admitted that certain elements derived from the air must be super-added to the water but we now know that other elements must be supplied by the earth if plants are to thrive and multiply the amount of materials contained in the atmosphere suited to the nourishment of plants is limited but it must be abundantly sufficient to cover the whole surface of the earth with a rich vegetation under the tropics and in those parts of our globe where the most genial conditions of fertility exist a suitable soil a moist atmosphere and high temperature vegetation is scarcely limited by space and where the soil is wanting it is gradually supplied by the decaying leaves bark and branches of plants it is obvious there is no deficiency of atmospheric nourishment for plants in those regions nor are these wanting in our own cultivated fields all the plants require for their development is conveyed to them by the incessant motions of the atmosphere the air between the tropics contains no more than that of the arctic zones and yet how different is the amount of produce an equal surface of land in the two situations this is easily explicable all the plants of tropical climes the oil and wax palms the sugarcane etc contain only a small quantity of the elements of the blood necessary to the nutrition of animals as compared with our cultivated plants the tubers of the potato in chilli its native country where the plant resembles a shrub if collected from an acre of land would scarcely suffice to maintain an irish family for a single day Darwin the result of cultivation in those plants which serve as food is to produce in them those constituents of the blood in the absence of the elements essential to these in the soil starch sugar and woody fiber are perhaps formed but no vegetable fibrin albumin or casein if we intend to produce on a given surface of soil more of these latter matters than the plants can obtain from the atmosphere or receive from the soil of the same surface in its uncultivated and normal state we must create an artificial atmosphere and add the needed elements to the soil the nourishment which must be supplied in a given time to different plants in order to admit a free and unimpeded growth is very unequal on pure sand on calcaria soil on naked rocks only a few genera of plants prosper and these are for the most part perennial plants they require for their slow growth only such minute quantities of mineral substances as the soil can furnish which may be totally barren for other species annual and especially summer plants grow and attain their perfection in a comparatively short time they therefore do not prosper on a soil which is poor in those mineral substances necessary to their development to attain a maximum in height in the short period of their existence the nourishment contained in the atmosphere is not sufficient if the end of cultivation is to be obtained we must create in the soil an artificial atmosphere of carbonic acid and ammonia and this surplus of nourishment which the leaves cannot appropriate from the air must be taken up by the corresponding organs i.e. the roots from the soil but the ammonia together with the carbonic acid are alone insufficient to become part of a plant destined to the nourishment of animals in the absence of the alkalis the phosphates and other earthly salts no vegetable fibrin no vegetable casein can be formed the phosphoric acid of the phosphate of lime indispensable to the seralia and other vegetables in the formation of their seeds is separated as an excrement in great quantities by the rind and barks of lignious plants how different are the evergreen plants the cacti the mosses the ferns and the pines from our annual grasses the seralia and leguminous vegetables the former at every time of the day during winter and summer obtain carbon through their leaves by absorbing carbonic acid which is not furnished by the barren soil on which they grow water is also absorbed and retained by their curious or fleshy leaves with great force they lose very little by evaporation compared with other plants on the other hand how very small is the quantity of mineral substances which they withdraw from the soil during their almost constant growth in a year in comparison with the quantity which one crop of wheat of an equal weight receives in three months it is by means of moisture that plants receive the necessary alkalis and salts from the soil in dry summers a phenomenon is observed which when the importance of mineral elements to the life of a plant was unknown could not be explained the leaves of plants first developed and perfected and therefore nearer the surface of the soil shrivel up and become yellow lose their vitality and fall off while the plant is in an active state of growth without any visible cause this phenomenon is not seen in moist years nor in evergreen plants and but rarely in plants which have long and deep roots nor is seen in perennials in autumn and winter the cause of this premature decay is now obvious the perfectly developed leaves absorb continually carbonic acid and ammonia from the atmosphere which are converted into elements of new leaves buds and shoots but this metamorphosis cannot be affected without the aid of the alkalis and other mineral substances if the soil is moist the latera continually supply to an adequate amount and the plant retains its lively green color but if this supply ceases from a want of moisture to dissolve mineral elements a separation takes place in the plant itself the mineral constituents of the juice are withdrawn from the leaves already formed and are used for the formation of the young shoots and as soon as the seeds are developed the vitality of the leaves completely ceases these withered leaves contain only minute traces of soluble salts while the buds and shoots are very rich in them on the other hand it has been observed that where a soil is too highly impregnated with soluble saline materials these are separated upon the surface of the leaves this happens to culinary vegetables especially whose leaves become covered in a white crust in consequence of these exudations the plant sickenes its organic activity decreases its growth is disturbed and if this state continues long the plant dies this is most frequently seen in fallacious plants the large surface of which evaporate considerable quantities of water carrots pumpkins peas etc are frequently thus diseased when after dry weather the plant being near its full growth the soil is moistened by short showers followed again by dry weather the rapid evaporation carries off the water absorbed by the root and this leaves the salt in the plant in a far greater quantity than it can assimilate these salts effloresce upon the surface of the leaves and if they are herbaceous and juicy produce an effect upon them as if they had been watered with a solution containing a greater quantity of salts then their organism can bear of two plants of the same species this disease befalls that which is nearest its perfection if one should have been planted later or be more backwards in its development the same external cause which destroys the one will contribute to the growth of the other end of section 11 section 12 of familiar letters on chemistry this is a LibriVox recording all LibriVox recordings are in the public domain for more information or to volunteer please visit LibriVox.org recording by Larissa Jaworski Brisbane Australia March 2007 familiar letters on chemistry by Justice Liebig letter 12 my dear sir having now occupied several letters with the attempt to unravel by means of chemistry some of the most curious functions of the animal body and as I hope made clear to you the distinctions between the two kinds of constituent elements in food and the purposes they severally subserve in sustaining life let me now direct your attention to a scarcely less interesting and equally important subject the means of obtaining from a given surface of the earth the largest amount of produce adapted to the food of man and animals agriculture is both a science and an art the knowledge of all the conditions of life of vegetables the origin of their elements and the sources of their nourishment forms its scientific basis from this knowledge we derive certain rules for the exercise of art the principles upon which the mechanical operations of farming depend the usefulness or necessity of these for preparing the soil to support the growth of plants and for removing every obnoxious influence no experience drawn from the exercise of the art can be opposed to true scientific principles because the latter should include all the results of practical operations and are in some instances solely derived therefrom theory must correspond with experience because it is nothing more than the reduction of a series of phenomena to their last causes a field in which we cultivate the same plant for several successive years becomes barren for that plant in a period varying with the nature of the soil in one field it will be in three in another in seven in a third in twenty in a fourth in a hundred years one field bears wheat and no peas another beans or turnips but no tobacco a third gives a plentiful crop of turnips but will not bear clover what is the reason that a field loses its fertility for one plant the same which at first flourished there what is the reason one kind of plant succeeds in a field where another fails these questions belong to science what means are necessary to preserve a field its fertility for one and the same plant what to render one field fertile for two or three for all plants these last questions are put by art but they cannot be answered by art if a farmer without the guidance of just scientific principles is trying experiments to render a field fertile for a plant which it otherwise will not bear his prospect of success is very small thousands of farmers try such experiments in various directions the result of which is a mass of practical experience forming a method of cultivation which accomplishes the desired end for certain places but the same method frequently does not succeed it indeed ceases to be applicable to a second or third place in the immediate neighborhood how large a capital and how much power are wasted in these experiments very different and far more secure is the path indicated by science it exposes us to no danger of failing but on the contrary it furnishes us with every guarantee of success if the cause of failure of barrenness in the soil for one or two plants has been discovered means to remedy it may be found the most exact observations prove that the method of cultivation must vary with the geognostical condition of the subsoil in basalt, graywack, porphyry, sandstone, limestone etc are certain elements indispensable to the growth of plants and in the presence of which renders them fertile this fully explains the difference in the necessary methods of culture for different places since it's obvious that the essential elements of the soil must vary with the varieties of composition of the rocks from the disintegration of which they originated wheat, clover and turnips for example each require certain elements from the soil they will not flourish where the appropriate elements are absent science teaches us what elements are essential to every species of plants analysis of their actions if therefore a soil is found wanting of any of those elements we discover it at once the cause of its barrenness and its removal may now be readily accomplished the empiric attributes all his success to the mechanical operations of agriculture he experiences and recognizes their value without inquiring what are the causes of their utility their mode of action and yet this scientific knowledge is of the highest importance for regulating the application of power and the expenditure of capital for ensuring its economic expenditure and the prevention of waste can it be imagined that the mere passing of the plough share or the harrow through the soil the mere contact of the iron can impart fertility miraculously nobody perhaps seriously entertains such an opinion nevertheless the modus operandi of these mechanical operations is by no means generally understood the fact is quite certain that careful ploughing exerts the most favorable influence the surface is thus mechanically divided changed increased and renovated but the ploughing is only auxiliary to the end sought in the effects of time in what in agriculture technically called fellows the repose of the fields we recognize by science certain chemical actions which are continually exercised by the elements of the atmosphere upon the whole surface of our globe by the action of its oxygen and its carbonic acid aided by water rain changes of temperature etc certain elementary constituents of rocks or of their ruins which forms the soil capable of cultivation are rendered soluble in water and consequently become separable from all their insoluble parts these chemical actions poetically denominates the tooth of time destroy all the works of man and gradually reduce the hardest rocks to the condition of dust by their influence the necessary elements of the soil become fitted for assimilation by plants and it's precisely the end which is obtained by the mechanical operations of farming they accelerate the decomposition of the soil in order to provide a new generation of plants with the necessary elements in a condition favorable to their assimilation it is obvious that the rapidity of the decomposition of a solid body must increase with the extension of its surface the more points of contact we offer in a given time to the external chemical agent the more rapid will be its action the chemist in order to prepare a mineral for analysis to decompose it or to increase the solubility of its elements proceeds in the same way as the farmer deals with his fields he spares no labor in order to reduce it to the finest powder he separates the impalpable from the coarser parts by washing and repeats his mechanical bruising and trituration being assured his whole process will fail if he is inattentive to this essential and preliminary part of it the influence which the increase of surface exercises upon the integration of rocks and upon the chemical action of air and moisture is strikingly illustrated upon a large scale in the operations pursued by the gold mines of yakwell in chili these are described in a very interesting manner by darwin the rock containing the gold ore is pounded by mills into the finest powder this is subjected to washing which separates the lighter particles from the metallic the gold sinks to the bottom while a stream of water carries away the lighter earthy parts into ponds where it subsides to the bottom as mud when this deposit has gradually filled up the pond this mud is taken out and piled in heaps and left exposed to the action of the atmosphere and moisture the washing completely removes all the soluble part of the disintegrated rock the insoluble part moreover cannot undergo any further change while it is covered with water and so excluded from the influence of the atmosphere at the bottom of the pond but being exposed at once to the air and moisture a powerful chemical action takes place in the whole mass which becomes indicated by an efflorescence of salts covering the whole surface of the heaps in considerable quantity after being exposed for two to three years the mud is again subject to the same process of washing and a considerable quantity of gold is obtained this having been separated by the chemical process of decomposition in the mass the exposure and washing of the same mud is repeated six or seven times and at every washing it furnishes a new quantity of gold although its amount diminishes every time precisely similar is the chemical action which takes place in the soil of our fields and we accelerate and increase it by the mechanical operations of our agriculture by these we sever and extend the surface and endeavor to make every atom of the soil accessible to the action of carbonic acid and oxygen of the atmosphere we thus produce a stock of soluble mineral substances which serves as nourishment to a new generation of plants materials which are indispensable to their growth and prosperity end of section 12 section 13 of familiar letters on chemistry this is a LibriVox recording all LibriVox recordings are in the public domain for more information or to volunteer please visit LibriVox.org recording by Larissa Jaworski, Brisbane Australia March 2007 familiar letters on chemistry by Justice Liebig letter 13 my dear sir having in my last letter spoken of the general principles on upon which the science and art of agriculture must be based let me now direct your attention to some of those particulars between chemistry and agriculture and demonstrate the impossibility of perfecting the important art of rearing food for man and animals without a profound knowledge of our science all plants cultivated as food require for their healthy sustenance the alkalis and alkaline earths each in a certain proportion and in addition to these the sorrelia do not succeed in a soil destitute of silica in a soluble condition the combinations of this substance found as natural productions namely the silicates differ greatly in the degree of facility with which they undergo decomposition in consequence of their unequal resistance opposed by their integral parts to the dissolving power of the atmospheric agencies. Thus the granite of Corsica degenerates into a powder in time which scarcely suffices to deprive the polished granite of Heidelberg of its luster. Some soils abound in silicates so readily decomposable that in every one or two years as much silicate of potash becomes soluble and fitted for assimilation as is required by the leaves and straw of a crop of wheat. In Hungary extensive districts are not uncommon where wheat and tobacco have been grown alternately upon the same soil for centuries. The land never receiving back any of those mineral elements which were withdrawn in the grain and straw. On the other hand there are fields in which the necessary amount of soluble silicate of potash for a single crop of wheat is not separated from the insoluble masses in the soil less than two, three or even more years. The term fellow in agriculture designates that period in which the soil left to the influence of the atmosphere becomes enriched with those soluble mineral constituents. Fellow however does not generally imply the entire cessation of cultivation but only an interval in the growth of the soralia. That store of silicates and alkalis which is the principal condition of their success is obtained. If potatoes or turnips are grown upon the same fields in the intermediate periods since these crops do not abstract a particle of silica and therefore leave the field equally fertile for the following crop of wheat. The preceding remarks will render it obvious to you that the mechanical working of the soil is the simplest and cheapest method of rendering the elements of nutrition contained in it accessible to plants. But it may be asked are there not other means of decomposing the soil besides its mechanical subdivision? Are there not substances which by their chemical operation will equally well or better render its constituents suitable for entering into vegetable organisms? Yes we certainly possess such substances and one of them namely quick lime has been employed for the last century past in England for this purpose. And it would be difficult to find a substance better adapted to this service as it is simple and in almost all localities cheap and easily accessible. In order to obtain correct views respecting the effort of quick lime upon the soil let me remind you of the first process employed by the chemist when he is desirous of analysing a mineral and for this purpose wishes to bring its elements into a soluble state. Let the mineral to be examined be for instance feldspar. This substance taken alone even when reduced to the finest powder requires for its solution to be treated with an acid for weeks or months but if we first mix it with quick lime and expose the mixture to a moderately strong heat the lime enters into chemical combination with certain elements of the feldspar and its alkali or potas is set free. And now the acid even without heat dissolves not only the lime but also so much of the silica of feldspar as to form a transparent jelly. The same effect which the lime in this process with the aid of heat exerts upon the feldspar it produces when it's mixed with the alkali agrylaceous silicates and they are for a long time kept together in a moist state. Common potas clay or pipe clay diffused through water and added to the milk of lime thickens immediately upon mixing and if the mixture is kept for some months then treated with acid the clay becomes gelatinous which would not occur without the admixture with the lime. The lime in combining with the elements of the clay liquefies it and what is more remarkable liberates the greater part of its alkalis. These interesting facts were first observed by Fuchs and Munich. They have not only led to a more intimate knowledge of the nature and properties of the hydraulic cements but what is far more important they explain the effects of caustic lime upon the soil and guide the agriculturist in the application of an invaluable means of opening it and setting free its alkalis. Substances so important they're so indispensable to its crops. In the month of October the fields of Yorkshire and Oxfordshire look as if they were covered with snow. Whole square miles are seen whitened over with quick lime which during the moist winter months exercises its beneficial influence upon the stiff clay-y soil of those counties. According to the humus theory quick lime ought to exert the most noxious influence upon the soil because all organic matters contained in it are destroyed by it and rendered incapable of yielding their humus to a new vegetation. The facts are indeed directly contrary to this now abandoned theory. The fertility of the soil is increased by the lime. The sorrelia require the alkalis and alkaline silicates which the action of the lime renders fit for assimilation by the plants. If in addition to these there is any decaying organic matter present in the soil supplying carbonic acid it may facilitate their development but it is not essential to then growth. If we furnish the soil with ammonia and the phosphates which are indispensable to the sorrelia with the alkaline silicates we have all the conditions necessary to ensure an abundant harvest. The atmosphere is an inexhaustible source of carbonic acid. A no less favourable influence than that of lime is exercised upon the soil of PT land by the mere act of burning it. This greatly enhances its fertility. We have not long been acquainted with the remarkable change with which the properties of clay undergo by burning. The observation was first made in the process of analysing the clay silicates. Many of these in their natural state are not acted on by acids but they become perfectly soluble if heated to redness before the application of the acid. This property belongs to Potter's clay, pipe clay, loam and many different modifications of clay in soils. In the natural state they may be boiled in concentrated sulfuric acid without sensible change but if feebly burned as is done with the pipe clay in many alum manufacturers they dissolve in the acid with the greatest facility the contained silica being separated like jelly in a soluble state. Potter's clay belongs to the most sterile kinds of soil and yet it contains within itself all the constituent elements essential to a most luxurious growth of plants but their mere presence is insufficient to secure this end. The soil must be accessible to the atmosphere, to its oxygen, to its carbonic acid. They must penetrate it in order to secure the conditions necessary to a happy and vigorous development of the roots. The elements present must be brought into this particular state of combination which will enable them to enter into plants. Plastic clay is wanting in these properties but they are imparted to it by a feeble calcination. At Hardwick Court near Gloucester I have seen a garden, Mr Baker's, consisting of a stiff clay which was perfectly sterile become by mere burning extremely fertile. The operation was extended to a depth of three feet. This was an expensive process certainly but it was effectual. The great difference in the properties of burnt and unburnt clay is illustrated by what is seen in brick houses built in moist situations. In the town of Flanders for instance where most buildings are brick efflorescences of salts cover the surfaces of the walls like a white nap within a few days after they are erected. If this saline incrustation is washed away by the rain it soon reappears and this is even observed on walls which like the gateway of Lyle have been erected for centuries. These saline incrustations consist of carbonates and sulphates with alkaline bases and it is well known that these act an important part in vegetation. The influence of lime in their production is manifested by their appearing first at the place where the mortar and brick come into contact. It will now be obvious to you that in a mixture of clay with lime all the conditions exist for the solution of the silicated clay and the solubility of the alkaline silicates. The lime gradually dissolving in water charged with carbonic acid acts like milk of lime upon the clay. This explains also the favorable influence which mal by which term all those varieties of clay rich in chalk are designated exerts upon most kinds of soil. There are Mali soils which surpass all others in fertility for all kinds of plants but I believe mal in a burnt state must be far more effective as well as other materials possessing a similar composition as for instance those species of limestone which are adapted to the preparation of hydraulic cements. For these carry to the soil not only the alkaline bases useful to plants but also silica in a state capable of assimilation. The ashes of coals and lignite are also excellent means of amyloriating the soil and they are used in many places for this purpose. The most suitable may be ready readily known by their property of forming a gelatinous mass when treated with acids or by becoming when mixed with cream of lime like hydraulic cement solid and harder stone. I have now I trust explained to your satisfaction that the mechanical operations of agriculture the application of lime and chalk to lands and the burning of clay depend upon one and the same scientific principle. They are means of accelerating the decomposition of the alkaline clay silicates in order to provide plants at the beginning of a new vegetation with certain inorganic matters indispensable for their nutrition. End of section 13. Section 14 of Familiar Letters on Chemistry This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer please visit LibriVox.org. Familiar Letters on Chemistry by Justice Libig. Letter 14. Nature and Effects of Maneuvers Animal bodies subject to constant waste. Parts separating. Exuviae waste vegetable matters. Together all contain the elements of the soil and of food. Various value of excrement of different animals as manure. My dear sir, I treated in my last letter of the means of improving the condition of the soil for agricultural purposes by mechanical operations and mineral agents. I have now to speak of the uses and effects of animal exuviae and vegetable matters or manures properly so-called. In order to understand the nature of these and the peculiarity of their influence upon our fields it is highly important to keep in mind the source whence they are derived. It is generally known that if we deprive an animal of food the weight of its body diminishes during every month of its existence. If this abstinence is continued for some time the diminution becomes apparent to the eye. All the fat of the body disappears, the muscles decrease in firmness and bulk, and if the animal is allowed to die starved scarcely anything but skin, tendon and bones remain. This emanciation which occurs in a body otherwise healthy demonstrates to us that during the life of an animal every part of its living substance is undergoing a perpetual change. All its component parts, assuming the form of lifeless compounds, are thrown off by the skin, lungs, and urinary system, altered more or less by the respiratory organs. This change in the living body is intimately connected with the process of respiration. It is in truth occasioned by the oxygen of the atmosphere and breathing which combines with all the various matters within the body. At every inspiration a quantity of oxygen passes into the blood in the lungs and unites with its elements, but although the weight of the oxygen thus daily entering into the body amounts to thirty-two or more ounces, yet the weight of the body is not thereby increased. Exactly as much oxygen as is imbibed in inspiration passes off in expiration, in the form of carbonic acid and water, so that with every breath the amount of carbon and hydrogen in the body is diminished. But the emanciation, the loss of weight by starvation, does not simply depend upon the separation of the carbon and hydrogen, but all the other substances which are in combination with these elements in the living tissues pass off in the secretions. The nitrogen undergoes a change and is thrown out of the system by the kidneys. Their secretion, the urine, contains not only a compound rich in nitrogen, namely urea, but the sulfur of the tissues in the form of a sulfate. All the soluble salts of the blood and animal fluids, common salt, the phosphates, soda, and potash. The carbon and hydrogen of the blood, of the muscular fiber, and of all the animal tissues which can undergo change, return into the atmosphere. The nitrogen and all the soluble inorganic elements are carried into the earth in the urine. These changes take place in the healthy animal body during every moment of life. A waste and loss of substance proceeds continually, and if this loss is to be restored and the original weight and substance repaired, an adequate supply of materials must be furnished, from whence the blood and wasted tissue may be regenerated. This supply is obtained from the food. In an adult person, in a normal or healthy condition, no sensible increase or decrease of weight occurs from day to day. In youth the weight of the body increases, whilst in old age it decreases. There can be no doubt that in the adult the food has exactly replaced the loss of substance. It is supplied just so much carbon, hydrogen, nitrogen, and other elements as have passed through the skin, lungs, and urinary organs. In youth the supply is greater than the waste. Part of the elements of the food remain to augment the bulk of the body. In old age the waste is greater than the supply, and the body diminishes. It is unquestionable that, with the exception of a certain quantity of carbon and hydrogen, which are secreted through the skin and lungs, we obtain in the solid and fluid excrements of man and animals all the elements of their food. We obtain daily, in the form of urea, all the nitrogen taken in the food, both of the young and the adult, and further in the urine, the whole amount of the alkali's soluble phosphates and sulfates contained in all the various elements. In the solid excrements are found all those substances taken in the food which have undergone no alteration in the digestive organs. All indigestible matters such as woody fiber, the green coloring matter of leaves, chlorophyll, wax, etc. Physiology teaches us that the process of nutrition in animals, that is, their increase of bulk, or the restoration of wasted parts, proceeds from the blood. The purpose of digestion and assimilation is to convert the food into blood. In the stomach and intestines, therefore, all those substances in the food capable of conversion into blood are separated from its other constituents. In other words, during the passage of the food through the intestinal canal, there is a constant absorption of its nitrogen, since only azotized substances are capable of conversion into blood, and therefore the solid excrements are destitute of that element, except only a small portion in the constitution of that secretion which is formed to facilitate their passage. With the solid excrements the phosphates of lime and magnesium, which are contained in the food and not assimilated, are carried off, these salts being insoluble in water and therefore not entering the urine. We may obtain a clear insight into the chemical constitution of the solid excrements without further investigation by comparing the feces of a dog with his food. We give that animal flesh and bones substances rich in azotized matter, and we obtain as the last product of its digestion a perfectly white excrement, solid while moist, but becoming in dry air a powder. This is the phosphate of lime of the bones with scarcely one percent of foreign organic matter. Thus we see that in the solid and fluid excrements of man and animals, all the nitrogen, in short all the constituent ingredients of the consumed food, soluble and insoluble, are returned, and as food is primarily derived from the fields, we possess in those excrements all the ingredients which we have taken from it in the form of seeds, roots, or herbs. One part of the crops employed for fattening sheep and cattle is consumed by man as animal food. Another part is taken directly, as flour, potatoes, green vegetables, etc. A third portion consists of vegetable, refuse, and straw employed as litter. None of the materials of the soil need be lost. We can, it is obvious, get back all its constituent parts which have been withdrawn therefrom, as fruits, grains, and animals, in the fluid and solid excrements of man and the bones, blood, and skins of the slaughtered animals. It depends upon ourselves to collect carefully all these scattered elements and to restore the disturbed equilibrium of composition in the soil. We can calculate exactly how much and which of the component parts of the soil we export, in a sheep or an ox, in a quarter of barley, wheat, or potatoes, and we can discover, from the known composition of the excrements of man and animals, how much we have to supply to restore what is lost to our fields. If, however, we could procure from other sources the substances which we give to the exuviae of man and animals their value in agriculture, we should not need the latter. It is quite indifferent for our purposes whether we supply the ammonia, the source of nitrogen, in the form of urine, or in that of a salt derived from coal-tar, whether we derive the phosphate of lime from bones, appetite, or fossil excrements. The principal problem for agriculture is how to replace those substances which have been taken from the soil and which can be furnished by the atmosphere. If the manure supplies an imperfect compensation for this loss, the fertility of a field or of a country decreases. If, on the contrary, more are given to the fields, their fertility increases. An importation of urine or of solid excrements from a foreign country is equivalent to an importation of grain and cattle. In a certain time the elements of those substances assume the form of grain or of fodder, then become flesh and bones, enter into the human body, and return again day by day to the form they originally possessed. The only real loss of elements we are unable to prevent is of the phosphates and these in accordance with the customs of all modernations are deposited in the grave. For the rest every part of that enormous quantity of food which a man consumes during his lifetime, say in sixty or seventy years, which was derived from the fields, can be obtained and returned to them. We know with absolute certainty that in the blood of a young or growing animal there remains a certain quantity of phosphate of lime and of the alkaline phosphates to be stored up and to minister to the growth of the bones and general bulk of the body, and that, with the exception of this very small quantity, we receive back in the solid and fluid excrements all the salts and alkaline bases, all the phosphates of lime and magnesium, and consequently all the inorganic elements which the animal consumes in its food. We can thus ascertain precisely the quantity, quality, and composition of animal excrements without the trouble of analyzing them. If we give a horse daily four and a half pounds weight of oats and fifteen pounds of hay, and knowing that the oats give four percent and hay nine percent of ashes, we can calculate that the daily excrement of the horse will contain twenty one ounces of inorganic matter which was drawn from the fields. By analysis we can determine the exact relative amount of silica of phosphates and of alkalis contained in the ashes of the oats and of the hay. You will now understand that the constituents of the solid parts of animal excrements and therefore the qualities as manure must vary with the nature of the creature's food. If we feed a cow upon beetroot or potatoes without hay, straw, or grain there will be no silica in her solid excrements, but there will be phosphate of lime and magnesium. Her fluid excrements will contain carbonate of potash and soda, together with compounds of the same bases with inorganic acids. In one word we have, in the fluid excrements, all the soluble parts of the ashes of the consumed food, and in the solid excrements all those parts of the ashes which are insoluble in the water. If the food after burning leaves behind ashes containing soluble alkaline phosphates, as is the case with bread, seeds of all kinds, and flesh, we obtain from the animal by which they were consumed a urine holding in solution these phosphates. If, however, the ashes of food contain no alkaline phosphates, but abound in insoluble earthly phosphates as hay, carrots, and potatoes, the urine will be free from alkaline phosphates, but the earthly phosphates will be found in the feces. The urine of man, of carnivorous and gramminivorous animals, contain alkaline phosphates. That of herbivorous animals is free from these salts. The analysis of the excrements of man, of the pisivorous birds, as the guano, of the horse, and of cattle furnishes us with the precise knowledge of the salts they contain, and demonstrates that in those excrements we return to the fields, the ashes of the plants which have served as food, the soluble and insoluble salts and earths indispensable to the development of cultivated plants, and which must be furnished to them by a fertile soil. There can be no doubt that, in supplying these excrements to the soil, we return to it those constituents which the crops have removed from it, and we renew its capability of nourishing new crops. In one word we restore the disturbed equilibrium, and consequently knowing that the elements of the food derived from the soil enter into the urine and solid excrements of the animals it nourishes, we can, with the greatest facility, determine the exact value of the different kinds of manure. Thus the excrement of pigs which have been fed with peas and potatoes are principally suited for manuring crops of potatoes and peas. In feeding a cow upon hay and turnips we obtain a manure containing the inorganic elements of grasses and turnips, and which is therefore preferable for manuring turnips. The excrement of pigeons contains the mineral elements of grain, that of rabbits the elements of herbs and kitchen vegetables. The fluid and solid excrements of man, however, contain the mineral elements of grain and seeds in the greatest quantity, and