 Hi, and welcome back to history and philosophy of science and medicine. I'm Matthew J. Brown This week we're talking about an article or chapter rather by Goldstein and Goldstein on John Snow on cholera, right? This chapter gives us some interesting insight into the nature of the scientific process and it tells the story of an important episode in the history of science and medicine sort of like founding episode or the founding sort of example of modern epidemiology. In this case also I think helps us think about the historiography of science and medicine. That is how the history is written. And so that's actually where I'd like to start and you know first let's get this out of the way. We're talking about not this John Snow, but this John Snow. Okay. So that's a pretty crucial difference. So we're going to talk first about what is the history of science and how is it done, right? What are the ways in which history of science is done? So history of science, maybe this is obvious, it's the study of the development over time of scientific knowledge. Whereas the historiography of science is the study of the methods of historians of science, which is sort of what we're talking about now. Now this week's reading is interesting in so far as it it leans heavily on John Snow's own words, right? Lots of long quotes from Snow's original manuscripts. And for the most part history works this way. It relies heavily on documentary evidence and archival evidence, the published and unpublished records of the time, right? So this chapter by quoting so heavily from Snow's own writing gives you a good sense of what the work of the historian consists in, right? Looking at the historical record, interpreting it, trying to understand what took place. You know, here we're getting a direct narrative from Snow. And as a piece of scientific writing, Snow's is interesting and it's different from how science is often written today because Snow talks a lot more realistically and in detail about the process that he went through, about the way the evidence was collected, the results that were obtained, also the way he thought through the issue and came up with his ideas, right? So that's a key element to how he wrote. Not so common to write the scientific paper that way anymore. But it helps us reconstruct things, historically speaking, a little more easily. Now, one approach to history that many historians are opposed to is what's sometimes called WIG history or the WIG interpretation of history. You see this term thrown around a lot, especially in history of science. WIG history studies the past, not only in the context of the present, but in order to glorify the present, right? It crafts historical narratives that not only center on the present, but treat the present as the product of an inevitable progression or even a heroic progression, right? So WIG histories often have heroes and villains in them, right? The heroes who advance the progression towards where we are now or the villains who stand in the way, right? And, you know, the WIGs were a political party in the UK that was particularly focused on, you know, the power of parliament over the power of the king. And the details of that are not so important. But you can see how, you know, a kind of partisan history can present present things that favors the current arrangement, right? So in history of science, this is a controversial issue. You should science be presented as progressive or should the historian be neutral with respect to questions of progress is a key question for historians of science. I mean, on the one hand, what they're talking about is the history of scientific knowledge and knowledge is an achievement. So you might think, well, it's inevitable that you do some amount of WIG history. On the other hand, you know, does that distort our understanding of what happened? So a major aspect of this is whether the historian should acknowledge that we what we currently believe to be the truth of the matter, right? And you see this in this chapter, right? The history of snow's research is presented, you know, early on with the bald statement, cholera is a bacterial disease. And we get a sense, you know, of what snow got right and what snow got wrong in our current lights, right? What he missed from the present understanding of the disease. Now, is this the right way to tell the history or should historians confine themselves to the information that would have been available to snow and others at the time as they try to understand what happened? That's a controversial question for historians of science. And I don't have an easy answer for it, but it's something to think about. You know, there's a as an aside here, I think we can we can ask about snow's own telling of history because he begins his manuscript and the and the and the chapter quotes from this with a little bit of history, right? Snow says the existence of Asiatic cholera cannot be distinctly traced back further than the year 1769. Previous to that time, the greater part of India was unknown to European medical men, right? And so this is kind of the this is kind of the origin of of cholera according to snow, right? But, you know, it's worth thinking about what is the perspective that snow is telling this history from? What kind of information is he leaving out? How is he restricting the materials he's looking at, right? And that helps us sort of that's a sort of historiographic critique that's important to understanding the way history is understood historically, right? And just as a hint, you know, you look at this passage and think might there have been some people somewhere who knew something about cholera in India before the European medical men that snow is referencing. So the the episode here of Snow's research on cholera, I think it has a lot to tell us about the relationship between hypothesis and evidence in science. And there's two common ways we talk about this. These the relationship between hypothesis and evidence, right? The one is inductivism, right? It tells us that evidence kind of comes first and what scientific hypotheses are generalizations from evidence, right? So you look at a number of scientists and philosophers have argued that the way that we come up with scientific knowledge is we look, you know, at one example, two examples, three examples, you know, this raven is black, that raven is black, that raven is black. I've got, you know, four hundred examples of observations of ravens that are black. Therefore, all ravens are black, right? It's a kind of inductive leap. The other kind of common way we think about evidence in science is what philosophers of science call hypothetical deductivism, right? According to which the hypothesis comes first, right? That's the hypothetical. And then we create tests to confirm or falsify the hypothesis based on the observational implications of the hypothesis. That's the deductivism, right? So we have a general claim like all ravens are black and then we generate a consequence of that, which is if we observe this raven, it will be black and then we test that, right? And one of the things that is, I think, significant here is that these simple views just don't seem to fit with the story of Snow's research. So one of the things that evidence is used for in Snow's research is, goes before even the notion of a hypothesis is the sort of statement of the problem, right? What is the question that the research is trying to answer in order to really formulate that Snow relies on all sorts of evidence of specific cases? And before he posits an initial hypothesis, he presents evidence that sort of is suggestive of that hypothesis, right? So the problem in question, of course, is, what are the causes of cholera and its spread, right? And how can its spread be prevented? The initial hypothesis has to do with the morbid matter that is ingested from one person to another that is sort of communicated and ingested. So Snow starts by gathering all sorts of evidence, comes up with a problem, comes up with a hypothesis, but apparently contradictory evidence is not taken by Snow to refute the hypothesis. So you might say, well, this evidence supports it, but this doesn't, so it's not gonna work out. Rather, what Snow does is he refines his hypothesis, he posits additional explanatory hypotheses such as the spread through the water supply, right? So, you know, we see in the poor population, people come into contact with sort of the bodily fluids of sick people through everyday means. Rich people don't do that, right? In Snow's account, they are in less close physical proximity, they have better hygiene at this time, but the spread through the water supply explains why rich people also get it when they do get it, right? So, and in fact, an important part of this story that our traditional way of talking about hypothesis and evidence wouldn't lead us to expect is the hypothesis in question actually control the collection of evidence itself, right? How, which evidence is seen as significant and where Snow goes to look for evidence, not just as a test, but as a way of further refining that hypothesis. So, we can see how the hypothesis of the water supply leads Snow to make various observations about water use, right? Try to understand what's really going on here. So, the discussion of the different habits of water used by the English and the Scots in order to explain different cholera patterns among them, cholera outbreak patterns among them is an important part of this. Now, because the collection of evidence is guided by the hypotheses that Snow is making, which in turn, you know, the hypothesis seeks to answer a certain question or solve a specific problem. This also explains certain gaps in the research, right? So, Snow, Goldstein and Goldstein point out, Snow came very close to recognizing a treatment for cholera, but he fell short here, primarily because the problem was how was cholera communicated and how can it be contained and not how can it be treated, right? That wasn't what Snow was concerned about. And so that lead him, led him to ignore certain kinds of important evidence to the latter question. Another interesting thing here that's worth mentioning is that Snow is able to provide compelling arguments about what causes cholera disease and what causes it to spread from person to person without using experiments to directly manipulate the factors, right? So, often in science and medicine, we establish causation through experimentation, right? We manipulate one variable, we measure another to determine the relationship, right? You are familiar with the slogan probably, correlation is not causation or correlation does not imply causation, right? So, simple like observational correlations are typically thought of as not enough, you need experimental evidence. But all Snow has in his data and his body of evidence are very particular kinds of correlational observational evidence, right? So, let's talk about two examples and here they're examples that come close to but don't ever quite become experiments, right? The first is the case of the Broad Street Pump, right? So, there's this localized outbreak in this part of London in 1854 near the Golden Square and Broad Street where there's a high incidence of cholera. Snow uses this map here to indicate a number of things. He shows here the number of cases, right? In with these little hash marks. Let me zoom in on that. So, you can see these hash marks here stacked up. These are the number of cases or deaths from cholera in those particular areas, right? So, Snow proposed a kind of public health experiment here. Okay, well, so first of all, Snow's hypothesis about water supply says we should look for a source of the outbreak and he centers things on this pump, right? This water pump on Broad Street. So, in this part of the city, people didn't have running water in their house and so if they wanted water, they had to go fill containers from this public water pump, right? So, Snow proposed a public health experiment, right? Remove the handle to the pump, right? Require people to go elsewhere to get water from other wells and see if the outbreak dies down, right? When they have to go elsewhere. Unfortunately, Snow had trouble getting the council to agree, right? So, by the time the handle was removed, the disease had basically run its course. So, the skeptic might say, okay, well, no correlation or it is, it's just correlation. So, it's not causation, right? So, you can't really conclude that the water supply was the source, right? You know, incidentally, just as a sort of historical marker, the pump is still there in the original location. You can see there it is without a handle on it. It's outside a pub that's now been called or named the John Snow. Broad Street weirdly has been renamed Broadwick Street. I'm not sure what's up that. But anyway, so the pump's still there. You can actually go see it next time you're in London. Okay, so, the Broad Street pump example, it provided some evidence, but you might, if you were skeptical, still deny that it was evidence that the water supply caused the outbreak, okay? So, a second major piece of evidence that Snow refers to came in the 1853, 1854 cholera epidemic outbreak in London. This map here shows water companies, right? So, these are places where there was running water and where the water supply was provided by two different companies who competed, right? The Sutherkin-Volhall Company and the Lambeth Company. So, Sutherkin-Volhall is in blue, Lambeth is in red, and the Overlap Purple is where they're both involved, right? Let's zoom in a little bit on that. So, there you see, I've zoomed in and I've made the color a little darker. So, in that purplish area where there is, you know, Overlap, you might have houses very close to each other, even next door to one another in the same neighborhood, and you're getting water from two different sources, right? The Sutherkin-Volhall Company, right, had much higher death rates from cholera, according to Snow, and according to the evidence, actually, that Snow gathered. And Snow attributes this difference to the different sources of their water. So, the Sutherkin-Volhall Company, both companies drew the water from the River Thames that run through the middle, that runs through the middle of London. If you look at the bigger map, you see the river there on the north, right? So, we're looking at the south side of London and the river runs through the middle, the River Thames. Both companies were drawing their water from the Thames, but at a certain point, the Lambeth Company moved the place they were gathering the water from upstream of the city, whereas the Sutherkin-Volhall Company, they were drawing water from the Thames in the middle of the city. So, a lot of waste from the city was pouring into the river, and they were drawing water out of it, right? So, that's how the water became contaminated, and that's why, according to Snow, there were more deaths. Incidentally, when I lived in London for three months as a graduate student, that area of Camberwell on the map is where I rented a room. So, a very familiar area to me. So, the reading discusses this case in terms of the difference between what they call laboratory experiments and natural experiments, right? So, in a laboratory or a clinical trial or any other type of genuine experiment, you, the scientist, directly manipulates or assigns some variable that you think is the cause or explanation of a phenomenon that you're interested in, and then you measure the effect, right, of manipulating that variable. In a natural experiment, it's as if nature herself has set up the experiment. So, you don't do any direct manipulation, but you find a variable that's kind of randomly distributed in something like the way you would have assigned it, and then you look for differences in the results. So, although you can't assign water companies to houses, the random sort of result of free competition got you something like what you would have done, right? If you had done a real experiment. Now, we could learn a lot, obviously, by intentionally exposing subjects to different water sources, intentionally infecting them with cholera or intentionally tainted sources, and then seeing how it spreads, right? But, the disease is fatal in that time period. Even today, we have good treatments for it, but it's not pleasant. So, this is an ethically problematic, unacceptable thing. So, Snow was lucky to find the natural experiment in this case, and he could look sort of retrospectively and make the causal determination without having to do something unethical. Now, at the end of the manuscript, Snow makes a variety of public health recommendations for interventions to stop the spread of cholera. And you might think of these as the ultimate experimental test for his research. Not that these were experiments that Snow himself conducted, but these recommendations, when put into practice, did prevent cholera epidemics in places like London. And, you know, you might think that that's really where the tests of his research came into being, right? So, that's the case of John Snow and the research on cholera that kind of founded epidemiology. Of course, you know, it's important to point out that this is one example of science. So, we should wonder, you know, what can we conclude about how science itself works from one example, an important point to think about when we're doing history and philosophy of science together. But, insofar as, you know, we think Snow was on to something, it's important to look at his example as we sort of interrogate maybe simplistic pictures of how science works. So, that's it for today. I look forward to hearing what you think about this example and about the larger issues it raises. And so, I'll see you in our class discussion or I will continue the conversation with you on Discord or in the comments here. Otherwise, I will see you next week.