TYPHOID FEVER. 471 



cultures are seen under the microscope to be brownish- 

 yellow in color, spindle-shaped, and sharply circum- 

 scribed. When superficial they are larger and form a 

 bluish iridescent layer with notched edges. These colo- 

 nies are often described as resembling grape-vine leaves. 

 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 

 typhoid bacillus and the colon bacillus are identical, and 

 make it impossible to select a single colony of either 

 with 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-produc- 

 tion, etc., cause the colonies of the different 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 1 kgm. 

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

 to macerate in 1 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- 



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



