90 MICROBIOLOGY 



Loeffler's blood serum though there was some indication that 

 the granular types were more common on the synthetic me- 

 dium than on the blood serum. 



Bile medium. This medium described by Conradi l has 

 been recommended by Buxton and Coleman for the cultiva- 

 tion of bacteria from the blood. It is prepared as follows : 

 Ox bile 900 cc. 



Glycerin 100 cc. 



Peptone 20 grams 



Mix, distribute in small flasks, putting about 100 cc. in each,, 

 and sterilize by fractional sterilization. 



Solid media. The solid media are employed to isolate 

 different species and to study the character of the growth, 

 especially of individual colonies of bacteria. The usual solid 

 media are agar and gelatin. The striking difference between 

 the tAvo is that gelatin liquefies at body temperature whereas 

 agar is not liquefied below the boiling point. For this reason 

 gelatin is not used for the cultivation of bacteria at a high 

 (body) temperature. There are several methods for the 

 preparation of these media. The simplest is the addition of 

 the gelatin or agar to bouillon. In these media the essential 

 nutritive part is in the bouillon, the agar and gelatin being 

 used for the purpose of solidifying the media. Agar itself is 

 usually neutral in reaction but the gelatin is often decidedly 

 acid. There is considerable variation in the reaction of dif- 

 ferent brands of gelatin. Other solid media, such as blood 

 serum, egg and potato, are used to a considerable extent. 



The preparation of nutrient agar. Weigh out 12 grams 

 of agar and cut it into small pieces with a pair of scissors. 

 Put the finely cut agar into an agate-iron dish, add 300 cc. 

 of distilled water, and boil over a gas flame, with constant 

 stirring to prevent scorching, until the agar becomes a thick, 

 homogeneous substance. Then add 1000 cc. of bouillon. 2 

 Place the dish containing the mixed agar and bouillon in a 



Conradi. Deut. med. Woch., Bd. XXXII (1906). 



2 Moore. Am. Monthly Microscopical Journal, May 1890, p. 115.. 



