472 PA THOGENIC BA CTERIA . 



tralized to the same point as before. After filtration, the 

 medium receives the addition of i per cent, of potassium 

 iodid. It is filled into tubes and sterilized. 



When water or feces suspected of containing the ty- 

 phoid bacillus are mixed in this medium and poured 

 upon plates, no bacteria develop well except the colon 

 and typhoid bacilli. 



These two bacteria, however, differ very markedly in 

 their appearance upon the medium, for the colon bacillus 

 appears as usual in twenty-four hours, while at that time 

 the typhoid bacillus, if present, will have produced no 

 colonies discoverable by the microscope. 



It is only after forty-eight hours — long after the colon 

 colonies have attained considerable size and are conspic- 

 uous — that the little colonies of the typhoid bacillus 

 appear as small, round, shining, dew-like points, which 

 are finely granular and in marked contrast to their 

 coarsely granular predecessors. Unfortunately, many of 

 the small colonies that develop in Eisner's medium sub- 

 sequently prove to be those of the colon bacillus. 



Kashida x prefers to make the differential diagnosis by 

 observing the marked acid production of the Bacillus coli 

 upon a medium consisting of bouillon containing i^ per 

 cent, of agar, 2 per cent, of milk-sugar, 1.0 per cent, of 

 urea, and 30.0 per cent, of tincture of litmus. The cul- 

 ture-medium should be blue. When liquefied and inocu- 

 lated with the colon bacillus, poured into Petri dishes, 

 and stood for sixteen to eighteen hours in the incubator, 

 the blue color passes off and the culture-medium becomes 

 red. If a glass rod dipped in hydrochloric acid be held 

 over the dish, vapor of ammonium chlorid is given off. 

 The typhoid bacillus produces no acid in this medium, 

 and there is consequently no change in its color. 



For the differentiation of the typhoid bacillus from the 

 allied bacillary forms, Hiss 2 recommends the use of two 

 special media. The first consists of 5 grams of agar-agar, 



1 Centralbl. f. Bakt. u. Paristenk., Bd. xxi., Nos. 20 and 21, June 24, 1897. 



2 "Journal of Experimental Medicine, Nov., 1897, vol. ii., No. 6. 



