VIRUSES 



W. M. STANLEY, member of the rockefeller institute for 



MEDICAL RESEARCH, PRINCETON; MEMBER OF THE NATIONAL ACADEMY 



OF SCIENCES 



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|URING the past ten years there has converged on a group 

 of small, infectious, disease-producing entities, known as 

 viruses, an array of scientific talent almost as diverse in nature as the 

 Allied forces that were brought to bear on the Axis powers. The 

 viruses are responsible for many diseases of man, animals, plants, and 

 bacteria. There is no single criterion by means of which viruses can 

 be differentiated from bacteria, yet the virus group has been segregated 

 by means of certain general characteristics. Among the most important 

 of these are small size, the ability to reproduce or multiply when within 

 the living cells of a given host, the ability to change or mutate during 

 multiplication, and the inability to reproduce or grow on artificial 

 media. The sole means of recognizing the existence of a virus is 

 provided by the manifestations of disease which result from the growth 

 of the virus. Although pathologists have studied viruses for over 

 fifty years and have added much to our knowledge, the new attack on 

 viruses has been spearheaded by chemistry, chiefly biochemistry and 

 physical chemistry, and their allied disciplines. The impact of these 

 diverse disciplines on viruses has been accompanied by reverberations 

 and repercussions, which, however, bode ill for viruses and good for 

 scientific thought. Clcrtain dominant facts stand out in Ijold relief 

 and these are understood and accepted by chemists and pathologists 

 alike, but there is an undercurrent of indecision where neither feels 



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