230 BACTERIOLOGY. 



of identifying this organism is very great. In addition to 

 this, the variability constantly 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 

 is usually given as characteristic, may, with the same 

 .culture, at one time appear as the typical invisible de- 

 velopment, at another time it may grow in a way easily 

 to be seen with the naked eye ; the change of reaction 

 which it is said to produce in bouillon is sometimes 

 much more intense than at others. 



The only properties possessed by it that may be said 

 to be constant are its motility, the absence of indol- 

 production, and its growth on gelatin plates ; but there 

 are other organisms which possess these same character- 

 istics in a degree that renders their differentiation from 

 the typhoid organism a matter of extreme difficulty, if 

 not of impossibility. 



These points should be borne in mind in the exami- 

 nation of drinking-water supposed to be contaminated 

 by typhoid dejections, for the organisms which most 

 nearly approach the typhoid bacillus in growth and 

 morphology are just those organisms which would 

 appear in water contaminated from cesspools, i. e., the 

 organisms constantly found in the normal intestinal 

 tract. Even in the stools of typhoid-fever patients 

 the presence of these normal inhabitants of the intes- 

 tinal tract renders the isolation of the typhoid organisms 

 no small task. 



The spleen of a patient dead of typhoid fever is the 

 safest place from which to obtain cultures of this organ- 

 ism for study. But it must always be remembered that 



