INFECTIONS OF THE DIGESTIVE TRACT 181 



sion this small number assumes a new interest. It re- 

 mains for the future to definitely prove or disprove the 

 role of dysentery toxin in the causation of poliomyelitis. 

 I have endeavored to sketch with few words some 

 of our leading acquisitions and problems in the colon- 

 typhoid-dysentery group of bacteria while touching only 

 lightly the realm of hypothesis. It is certain that 

 research will distinguish further varieties possessing 

 interest for human pathology within this large group. 

 Nor can we doubt that the methods by which we now seek 

 to combat the infections due to members of this group 

 will gain in efficiency and precision. Our attention has, 

 perhaps, been too exclusively fixed on the specific excit- 

 ants, and the role played by associated bacteria must re- 

 ceive more study, for it is clear that they sometimes play 

 a significant part in determining the outcome of an infec- 

 tion. The difference that decides whether a man will 

 live or die must frequently be a slight one, looked at from 

 the standpoint of the processes of battle within the body. 

 To learn to recognize more clearly in what this difference 

 consists and how to use such knowledge to turn the tide 

 of warring forces to the advantage of the life that hovers 

 on the verge of extinction is among the problems which 

 intelligent, careful research will help us to solve. 



LIQUEFYING BACTERIA 



In the foregoing section has been considered very 

 briefly the highly important group of Gram-negative 

 microorganisms which do not liquefy gelatin and 

 which are facultative anaerobes. It is desired here 



