 Bismillahirrahmanirrahim. Dear students, my name is Professor Dr. Muhammad Alisha and we are going to talk about very interesting subjects which is Viralogy. Viralogy is the study of the viruses. So what is virus and how it's affecting our daily life? We will study this in detail. First of all, the viruses definition and its meaning. A lot of the names of the diseases have been evolved from the Latin words. So same is the case with the virus. Virus has been a Latin word and its meaning is poison which is given name by a burgeonic in 1897. Viruses are non-cellular particles made up of genetic materials which is DNA or RNA and proteins. These are very simple particles so they can just evade from the living cells. These are obligatory intracellular parasites. These are submicroscopic and smaller than bacteria and actually these are the smallest particles which are until now has been discovered for the disease point of view. They are present, they are causing the disease in all the animals and plants and human beings, every particles and they are of different sizes. So for the take-home question is this that can you tell us the different sizes of the viruses? It's clear we have just studied in before different different slides that viruses so you can just take this this slide and you can see about the viruses sizes which are given here. These are the viruses which we have given in these slides. These are the historical viruses which were discovered for the first time just like some viruses are 0.003 to 0.05 microns, very smallest ones. Then the tobacco mosaic virus it is the virus of the plants and discovered some years ago. We will study in the next slides. It's 1.1 to 1 microns. Then there are the bacteria, fungus, plant spores and then raindroplets. We can just give this size to compare the different sizes of the viruses. So here you can see that how much smaller are the viruses as compared to the other particles which are present in the atmosphere. So from here you can see about you can know about some introduction of the viruses and virus meaning from where it has been evolved and the virus sizes. In the last slide we have seen that viruses are the smallest particles which have been evolved until now and it's not easy to see it's not it's impossible to see them with the naked eyes. We will continue to study about the viruses.