152 INFECTIONS OF THE DIGESTIVE TRACT 



identity of the organisms in many instances makes it 

 clear that affections attributed to colon bacilli were thus 

 classed without sufficient justification. For example, 

 many instances of supposedly colon-bacillus diarrhoea 

 must almost certainly have been due to the dysentery 

 bacillus. Remembering the cultural similarities of certain 

 colon bacilli and dysentery bacilli, it is easy to under- 

 stand how confusion might have occurred when the 

 fermentative characters were left out of account, as 

 was usually the case. Even an organism so different 

 from B. coli as the bacillus of typhoid fever was con- 

 founded with it in the early days of bacteriology, when 

 limited cultural criteria alone were employed. Thus 

 progress in methods of identification has step by step 

 circumscribed the conception of the colon bacillus and 

 given it sharper definition. There are indications that 

 this process of circumscription has not reached its final 

 stage. 



It seems established that organisms having the cultural 

 fermentative and agglutinative characters of B. coli at 

 times are endowed with a degree of virulence for small 

 animals which does not pertain to colon bacilli derived 

 from healthy human individuals. Such pathogenic 

 bacilli have been found in great abundance in some 

 diarrhceal conditions and appear to have been the cause 

 of these acute derangements. It is not clear whether 

 in such cases the dominant normal organisms have 

 acquired increased irritant properties or whether there 

 has occurred a process of substitution by which organisms 

 present normally in small numbers or introduced from 



