272 BACILLUS TYPHOSUS. 



persists for three or four months if not too many other sapro- 

 phytic germs are contained in it. 



Repeated freezing and thawing does not affect the vitality 

 of the germ, but a ten-minute exposure to a temperature of 

 60 C. is invariably fatal. Neither can it resist desiccation. 

 Carbolic acid, in a 1 or 2 per cent, solution, has no effect on 

 the germ. This resistance to carbolic acid is utilized in 

 obtaining pure cultures. Dried in a thin layer, the typhoid 

 bacilli preserve their vitality on linen for from sixty to 

 seventy days, on wood for thirty-two days, and on buckskin 

 for eighty days. Hermetically sealed bouillon cultures 

 remain alive for more than a year. 



Isolation : Pure cultures can be procured from the feces of 

 typhoid patients, but not until the second week, and even 

 then with difficulty unless the feces contain very few contami- 

 nating germs. Repeated attempts may have to be made 

 before the organism is finally isolated. 



It is preferable to make the culture from the spleen or the 

 mesenteric lymph-glands or Peyer's patches of typhoid fever 

 cadavers, but the autopsy must be made as soon as possible. 



The method of making the pure culture is as follows : 

 Add a 0.05 per cent, solution of carbolic acid to each of 

 several tubes of liquefied gelatin. A small piece of tissue or 

 several loopfuls of feces are transplanted to tube No. 1. 

 Tube No. 2 is inoculated from tube No. 1, and tube No. 3 

 from tube No 2. The contents of each tube are then plated 

 or rolled. The saprophytes do not develop because of the 

 carbolic acid which has been added to the medium, but the 

 growth of the typhoid bacillus and Bacillus coli communis is 

 not interfered with in the least. The colonies of these two 

 varieties must be differentiated. 



In order to aid in this differentiation, Eisner uses a special 

 medium for plating. It is prepared as follows : 1 kilogram 

 of potato, preferably the small, red, German variety, is mace- 

 rated in 1 liter of water for twelve hours. The juice is 

 thoroughly expressed and filtered cold, to separate as much 

 starch as possible. The filtrate is boiled and filtered again. 

 The resulting clear fluid is neutralized by adding 2^- to 3 c.c. 

 of a decinormal solution of sodium hydrate to each 10 c.c, of 



