38 THE POPULAR SCIENCE MONTHLY 



other hand, a number, especially of experimental investigators, without 

 being able to accept as valid any of the claims as to the discovery of a 

 microorganism as the cause of human cancer, always pointed out the 

 possibility that microorganisms might at least in a certain number, per- 

 haps even in a majority of cases, be a factor in the production of cancer 

 and tried to find new experimental means to approach these problems; 

 accordingly on various occasions we pointed out the possibility that 

 ultra-microscopic, perhaps intracellular, microorganisms might induce 

 body cells, under certain conditions, to proliferate in such a manner 

 that cancer resulted. However, in no case of human cancer has the 

 causative significance of a microorganism so far been proven. We shall 

 see later on that in a certain kind of animal cancer this proof has 

 recently been supplied by Peyton Eous. 



