NUTRIENT MEDIA 



vessel very tightly, so that a vacuum may be maintained in the 

 latter by means of an air pump. 



Collodion sacs are sometimes used in animal experiments. 

 Bouillon cultures are placed within the 

 sacs, which are then inserted in the ab- 

 domen of an animal and left there. The 

 sac is made of coUodion because it is 

 non-absorbent and allows the bacterial 

 juices and products to osmose outward 

 and be absorbed by the animal, while the 

 animal fluids percolate into the sac. 

 There are several very ingenious ways of 

 making these sacs, but the details are too 

 elaborate to be described here. 



BOUILLON 



Bouillon or broth is the most useful of 

 all the nutrient media, since it is not only 

 used as a liquid medium, but by the addi- 

 tion of gelatine, or agar, it is converted 

 into solid media. 



There are two methods of making 

 bouillon: 



Method i. 



Take 500 grams of lean beef free from all fat, chop it fine and 

 cover with 1,000 c.c. of water, shake and place on the ice over- 

 night. Then squeeze the fluid out of the met by means of a 

 cloth, and supply enough water to make a litre. Inoculate this 

 meat juice with a fluid culture of the colon bacillus for the pur- 

 pose of fermenting the meat sugar. For this purpose the inocu- 

 lated juice is allowed to stand at room temperature overnight. 

 Bring to a boil and add 



10 grams of Witte's peptone. 

 5 grams common salt. 



FIG. 26. Kitasato 

 filter for filtering toxins. 

 (Williams.) 



