CHEMICAL PROPERTIES OF VIRUSES 



By W. M. Stanley 



Department of Animal and Plant Pathology 

 The Rockefeller Institute for Medical Research, Princeton, N. J. 



[With 6 plates] 



Six years ago over a hundred viruses were recognized, yet it would 

 have been virtually impossible to write then on the present subject, 

 for at that time practically nothing was known about the chemical 

 properties of viruses. These agents, which are responsible for untold 

 millions of illnesses and deaths amongst people, animals, and plants, 

 were recognized only by means of the diseases which they caused, 

 diseases such as smallpox, parrot fever, yellow fever, St. Louis en- 

 cephalitis, poliomyelitis, horse encephalomyelitis, foot-and-mouth 

 disease of cattle, louping ill of sheep, hog cholera, rabies, dog distem- 

 per, fowl pox, certain types of tumorous growths in fowls and other 

 animals, jaundice of silkworms, and various yellows and mosaic dis- 

 eases of plants. The general nature of the agents responsible for 

 such diseases was a matter of much conjecture. When placed in 

 certain living cells, these agents could multiply, mutate or undergo 

 variation to form new strains, and induce immunity. They seemed 

 to have many of the properties of very small living organisms such 

 as the bacteria; yet, unlike most bacteria, they were too small to be 

 seen by means of the ordinary microscope and could not be induced 

 to multiply in the absence of living cells. They were mysterious, 

 invisible somethings which, in the absence of living cells, appeared 

 as harmless and as lifeless as pebbles on the beach, but which, even 

 after years of inactivity, were ready to spring into action and cause 

 disease and death when introduced by chance or by design into cer- 

 tain living cells. By virtue of their ability to mutate or form variants, 

 they were able to change and adapt themselves to new surroundings 

 and conditions and thus not only to retain but to enlarge their place 

 in a changing world. The fact that the viruses were recognized only 

 by means of the diseases which tliey caused and the fact that these 

 diseases were becoming of increasing importance only served to add 



1 Reprinted by permission from The Scientific Monthly, vol. 53, September 1941, 



261 



