106 INFECTIONS OF THE DIGESTIVE TRACT 



conditions pertaining to a culture medium. For example, 

 Dunham obtained widely different appearances in growths 

 of the same typhoid bacillus when grown in gelatin 

 plates in which the gelatin possessed varying degrees of 

 concentration and slightly different chemical characters. 

 The morphological characters of organisms are cer- 

 tainly important to consider and must be known as 

 a matter of course in any study of bacteria, but within 

 groups of closely related organisms morphology itself 

 gives us little aid. The question of motility is one of a 

 good deal of importance and should always be considered. 

 In general within a group of colon-like organisms a high 

 grade of motility suggests pathogenicity, but the absence 

 of motility or a low grade of it does not point in the 

 opposite direction, since pathogenic types of bacilli in 

 the dysentery group presumably not distantly related 

 to the colon bacilli are non-motile. The determination 

 of the staining characters of the organism with the Gram 

 method is most helpful provided a uniform method of 

 procedure be employed. In the absence of a uniform 

 technique the Gram method is less good than a simple 

 stain, since it serves only to confuse. Of great impor- 

 tance for the classification of the bacteria of the gastro- 

 enteric tract, as of bacteria generally, are the biochemical 

 properties. These biochemical characters include the 

 cleavage abilities of the organism with special reference 

 to their action on the soluble carbohydrates 1 with the 

 production of acid and gas, their ability to produce indol 



1 The great importance of this method of studying bacteria 

 was first pointed out by Professor Theobald Smith in connection 

 with the differentiation of typhoid and colon bacilli. 



