64 THE CULTIVATION OF EACTfiRIA. 



III. The Most Commonly Used Special Culture -Media. 



In making final distinctions between the different species 

 of bacteria the following special media are occasionally used : 



1. The Peptone Solution. 



Dry peptone, 1 part; 



Sodium chloride, J " ; 



Distilled water, 100 parts. 



This is filtered, decanted into test-tubes, and sterilized in the 

 steam sterilizer. 



This preparation is chiefly used for determining whether the 

 bacteria secrete indol or not. It is necessary, therefore, to see 

 that the peptone preparation used be chemically pure, also 

 that the solution be free from the presence of carbohydrates. 



2. Glucose-, lactose-, and saccharose-bouillon. These are 

 made by adding to the bouillon after filtration and before ster- 

 ilization from 1 to 2 per cent, of the desired kind of sugar. 



3. Conradi's bile medium is prepared as follows : 



Take of fresh ox-bile, 900 c.c. ; 



Glycerin, 100 c.c. ; 



Peptone, 20 grams. 



Mix, divide off into suitable quantities, and sterilize by frac- 

 tional sterilization. 



4. Jackson's bile medium is used for isolation of B. coli and 

 B. typhosus. These bacilli, especially the latter, outgrow all 

 other bacteria in this medium. This medium consists of 

 undiluted ox-bile, containing 1 per cent, peptone and 1 per 

 cent, lactose. Fermentation tubes are filled with this medium 

 and sterilized by fractional sterilization. 



5. Dorsett's egg medium is especially used for cultivating 

 Bacilli tuberculosis. It is made as follows : 



1. The yolks and whites of a number of eggs are thor- 



oughly mixed in a wide-mouthed flask. 



2. For every four eggs add 25 c.c. distilled water. 



Strain through cloth. 



3. Place 10 c.c. in tubes, and slant at 73 C. for five hours 



on two days. 



