BACILLUS TYPHOSUS 495 



some extent the growth of organisms other than bacillus 

 typhosus, particularly those of the colon group. It is used 

 in the following manner: To test-tubes containing a known 

 aipount (8 to 10 c.c.) of peptone solution, "brilliant green" is 

 added in varying amounts so as to have a series of solutions 

 ranging in strength from one part of the green to 500,000, to 

 one part to 100,000 of the peptone solution. A convenient 

 stock solution of the "brilliant green" is 1 : 1000 in water. 

 From this such amounts are added to the tubes of peptone 

 solution as will give the desired series of dilutions. The 

 tubes of peptone solution should have been sterilized before 

 the green is added. When ready, one adds to each of these 

 tubes an amount of the substance under consideration: 

 if it be feces — a moderate loopful may be broken up in 1 c.c. 

 of bouillon and one or two loopfuls of this used; if it be water 

 or milk from 0.1 to 0.3 c.c. The amount best suited must 

 be determined by experiment. 



When inoculated the tubes are kept at body temperature 

 for from eighteen to twenty-four hours, when they are 

 ready for the " differential" or " selective" plating. 



The enriching media should be free of sugar. 



In the process of plating, specially prepared selective 

 media are used that aim to render evident to the naked eye 

 distinguishing differences between the colonies of bacillus 

 typhosus and those of other confusing organisms, Of a 

 number of special media employed for this purpose two have 

 proved very satisfactory — notably that recommended by 

 Drigalski and Conradi, and that by Endo. 



Method of v. Drigalski and Conradi.' — This method 

 aims to separate bacillus typhosus from bacillus coli on the 

 basis of their fermenting properties, in such a manner as not 



1 Zeitschrift filr Hygiene, 1902, Bd. xxxix, p. 288. 



