TYPHOID FEVER. 371 



The center of the superficial colonies is the only portion 

 which shows the yellowish-brown color. The margins 

 of the colony appear somewhat reticulated. The gelatin 

 is not liquefied. 



Unfortunately, the appearances of the colonies of the 

 Bacillus typhi and the Bacillus coli communis are iden- 

 tical, and make it next to impossible to select a single 

 colony of either with any certainty. The only solution 

 of the problem is to transfer a large number of colonies 

 to some culture-medium in which a characteristic of one 

 or the other species is manifested, and then study the 

 growth ; or to grow the colonies upon some special 

 medium in which differences, such as rapidity of growth 

 or acid-production, etc. cause the colonies of the differ- 

 ent species to assume characteristic appearances. 



A method recently suggested by Eisner 1 has materially 

 aided the separation of these allied bacteria by using a 

 culture-medium upon which the two bacilli develop dif- 

 ferently. 



The Eisner medium can be made by allowing i kgm. 

 of grated potatoes (the small red German potato is best) 

 to macerate in i liter of water over night. The juice is 

 carefully pressed out, and filtered cold to get rid of as 

 much starch as possible. The filtrate is now boiled and 

 filtered again. The next step is a neutralization, in 

 which Eisner used litmus as an indicator, and added 2.5- 

 3 c.cm. of a -^ normal solution of sodium hydrate to each 

 10 c.cm. of the juice. Abbott prefers to use phenol- 

 phthalein as an indicator. The final reaction should be 

 slightly acid. Ten per cent, of gelatin (no peptone or 

 sodium chlorid) is now dissolved in the solution, which 

 is boiled for the purpose, and must then be again neu- 

 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 tv- 

 phoid bacillus are mixed in this medium and poured 



1 Zeitschrift fur Hygiene, xxii., Heft I, 1895; Dec. 6, 1896. 



