488 APPLICATION OF METHODS OF BACTERIOLOGY 



theless, in certain essential details relating to its causation, 

 very far from satisfying. 



A number of other organisms appear botanically to be 

 closely related to the typhoid bacillus, and under the avail- 

 able culture methods for studying them they so closely 

 simulate it that the difficulty of identifying this organism 

 is sometimes very great. In addition the variability con- 

 stantly seen in pure cultures of the typhoid bacillus itself 

 in no way renders the task more simple. 



For example, the morphology of the typhoid bacillus 

 is conspicuously inconstant; its growth on potato which was 

 formerly considered unique, may, with the same stock, at 

 one time be the typical invisible development, at another 

 it is easily to be seen with the naked eye; and the change of 

 reaction which it is said to produce in bouillon is sometimes 

 much more intense than at others. The indol-producing 

 function, hitherto regarded as absent from this organism, 

 is now known to be occasionally demonstrable by ordinary 

 methods, and frequently by special methods of cultivation 

 (Peckham, I. c.). The only properties exhibited by it under 

 the usual conditions of cultivation that may be said to be 

 constant are its motility; its inability to cause gaseous fer- 

 mentation of glucose, lactose, or saccharose; its incapacity 

 for coagulating milk; and its growth on gelatin plates 

 but there are other bacilli which possess these same character- 

 istics to a degree that renders their differentiation from 

 the typhoid organism often a matter that requires the careful 

 application of all the different tests. 



The Agglutination Reaction. The nearest approach to a 

 trustworthy means of identification is the specific reaction of 

 typhoid bacilli with the blood of typhoid subjects. When 

 typhoid bacilli are brought in contact with the blood-serum 



