ISOLATING THE TYPHOID BACILLUS. 423 



logical peculiarities, and is so closely simulated in cer- 

 tain respects by a group of other organisms to which it 

 appears to be botanically related, that its identification, 

 especially outside the infected body, is usually a matter 

 of considerable difficulty and uncertainty. For these 

 reasons many efforts have been made to discover specific 

 reactions for the organism, and with this end in view 

 many methods have been devised for its isolation from 

 water, fseces, sewage, and other matters believed to con- 

 tain it. None of them, however, has given general 

 satisfaction, and many have proved wholly untrust- 

 worthy. Those worthy of some degree of confidence 

 are as follows : 



El&ner's method. The medium employed is an acid 

 mixture of gelatin, potato-juice, and potassium iodide. 

 It contains neither peptone nor sodium chloride. On 

 this medium it is claimed that the ordinary, rapidly 

 growing, 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 char- 

 acter 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 scarcely visible at the 

 end of twenty-four hours. After forty-eight hours the 

 latter appear under the low power of the microscope as 

 small, pale, finely granular, almost transparent bodies 

 easily distinguished from the coarser, brownish colonies 

 of the colon bacillus. 



While the method is useful, it has its limitations, 

 and is not always reliable. At times colon colonies 

 develop in a manner that may readily cause one to 



