INFECTIONS OF THE DIGESTIVE TRACT 109 



artificial culture media of the same composition and still 

 remain strikingly constant with respect to the activity of 

 the toxins produced. The aerobic or anaerobic charac- 

 ters of microorganisms are of great importance in the 

 classification of intestinal bacteria, since the putrefactive 

 processes in the digestive tract are carried on largely 

 through the agency of strict anaerobes. No study of the 

 bacteria of the gastro-enteric tract can be considered 

 thorough which does not take the strict anaerobes into 

 account. This, of course, involves the use of anaerobic 

 technique. Some highly aerobic bacteria, like the micro- 

 organisms of cholera and the bacilli of tuberculosis, 

 multiply very poorly under strictly anaerobic conditions. 

 The majority of pathogenic microorganisms in man are, 

 however, facultative anaerobes capable of growing under 

 anaerobic as well as aerobic conditions, although the anae- 

 robic growth may be much less active than the develop- 

 ment in the presence of air. The ability of organisms to 

 make spores is another feature which has to be taken into 

 consideration in any classification of bacteria. Most of 

 the strict anaerobes of the intestinal tract possibly 

 all of them are capable of sporulating under certain 

 conditions, and this is a feature of great significance for 

 their persistence in the gastro-enteric tract, since in the 

 absence of the ability to sporulate in the tract the vege- 

 tative forms might easily lose their hold and die out. Of 

 late years much attention has been given to the aggluti- 

 native properties of bacteria growing in the intestinal 

 tract, with results of great importance for the classifica- 

 tion of these bacteria. It was at first supposed that the 



