316 WENDELL M. STANLEY 



can hardly be called molecular in nature and which is rather more organismal or 

 cell-like in nature. Some of the baaerial viruses have a very complex morphology, 

 with a head and tail somewhat similar to tlie sperm of higher organisms. 



For a long time many investigators thought that the plant viruses differed 

 basically from viruses affecting animals and man. This idea stemmed mainly 

 from the fact that for twenty years all of the crystallizable viruses were plant 

 viruses. This idea had to be relinquished two years ago when my colleagues, 

 Carlton Schwerdt and Frederick Schaffer, obtained poliomyelitis virus, which 

 is a t}^pical animal or human virus, in crystalhne form. This was the first virus 

 affecting animals or man to be obtained in crystalline form, and it is interesting 

 to note that crystalline poliovirus was obtained just twenty years after the iso- 

 lation of tobacco mosaic virus in crystalline form. One other animal or human 

 virus has just been crystallized and this is crystalline Coxsackie virus obtained 

 by Dr. Mattem of the National Institutes of Health. 



Hundreds of viruses are known and more are being discovered every month, 

 yet only a dozen or so have been obtained in purified form. In view of the pos- 

 sibility that these may represent the more stable and more readily purified 

 viruses, one cannot be certain that a true picture of the chemical and physical 

 properties of viruses as a whole has been obtained as yet. However, I beheve 

 that we have sufficient sampling to be significant for the purposes of the present 

 discussion, for we already know that viruses may range from small crystallizable 

 animal, human or plant viruses, which are nucleoprotein molecules, through 

 intermediate structures consisting of nucleoprotein, hpid and carbohydrate, to 

 large structures possessing a morphology and composition similar to that of 

 accepted cellular organisms. All of these diverse structures are bound together 

 by one all-important property, that of being able to reproduce their own charac- 

 teristic structure when placed within certain living cells. They are all, in short, 

 by definition, alive. 



Now I am only too fully aware of objections that some may have to considering 

 a crystallizable nucleoprotein molecule as a hving agent. Some may feel that life 

 is a mystery which is and must remain beyond the comprehension of the human 

 mind. With these I must disagree. Some may believe that a living molecule is 

 contrary to rehgion. Here again I must disagree for I see no conflict whatsoever 

 between science and religion and I see no wrong in accepting a molecule as a 

 hving structure. To many scientists the diverse expressions of chemical structure 

 represent miracles, and our expanding knowledge of the wonders of nature 

 provides ample opportunities to express our faith and only serves to make us full of 

 humility. Some may prefer to regard a virus molecule in a crystal in a test tube 

 as a potentially hving structure and to restrict the term 'hving' to a virus during 

 the time that it is actually reproducing. I would have no serious objection to 

 this, for I am reminded of the facts that certain tapeworms a foot or so in length 

 can live and reproduce only in certain hosts and that even man himself can be 

 regarded as requiring rather special conditions for Hfe, yet no one objects to 

 accepting man and tapeworms as examples of hfe. I am also reminded that we 

 are taught that the essence of a thing is not what it is, but what it does and the 

 doing of something involves time, hence there may be good reason always to 



