ISOLATING THE TYPHOID BACILLUS. 353 



All the preceding points should be borne in mind in 

 the examination of drinking-water supposed to be con- 

 taminated 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 intes- 

 tinal 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 

 somewhat troublesome. 



BACILLUS. 



A number of special methods for the isolation of the 

 typhoid bacillus from mixtures, such as water, feces, 

 etc., that contain it have been recommended, but none 

 of them has given general satisfaction, and many have 

 proved to be entirely untrustworthy. That which has 

 perhaps attracted the most attention is the recently de- 

 vised medium of Eisner. It is an acid mixture of 

 gelatin, potato juice, and iodide of potash. It contains 

 no peptone, and no sodium chloride is added. On this 

 medium it is claimed that the ordinary, rapidly grow- 

 ing, liquefying saprophytes do not develop, and that the 

 colon bacillus and typhoid bacillus find it favorable for 

 growth. These are differentiated from one another by 

 the macroscopic and microscopic character of their 

 colonies i. e., the growth of the colon colonies differs 

 little or not at all from that seen on ordinary nutrient 

 gelatin, while that of the typhoid colonies is so slow 

 that they are hardly visible at the end of twenty-four 

 hours. After forty-eight hours they appear under the 



