MEDIA MAKING AND APPARATUS 265 



STEPS COMMON TO ALL VARIETIES. 



1. Infuse finely chopped lean round steak (beef) free from 

 fat, gristle, bone, etc., in cold water — proportions 1 gram muscular 

 tissue to 1 c.c. (or gram) of distilled water; weigh container and 

 contents; leave covered in ice-chest for 24 hours. (Example: 1000 

 grams meat with 1000 grains (or c.c.) water). 



2. Weigh container and contents, adding water to make up 

 any loss by evaporation ; (/. c, the meat plus the water should weigh 

 2000 grams) ; filter through canton flannel, squeezing the successive 

 small portions of the meat left on filter; the filtrate should weigh (or 

 measure) the same amount as the water added in No. 1. If less, 

 squeeze the meat more thoroughly; if more, reject the surplus. 



3. Add to the filtrate (known as " 1 to 1 meat infusion ") 

 2% by weight of dried commercial "peptone" (Witte's), i. e., 

 20 grams. (Note: Commercial "peptones" are really largely 

 albumose.) 



4. Heat over water bath until peptone is dissolved. The " 1 

 to 1 meat infusion plus peptone " should not be allowed to rise 

 above 50 C. during this process ; restore loss by evaporation, i. e. y 

 by weighing and restoring to original weight (1000 grams) by 

 addition of water. 



STEPS WHICH DIFFERENTIATE THE DIFFERENT MEDIA FROM EACH 



OTHER. 



5. (a) Plain nutrient broth : Add to " 1 to 1 meat infusion -f- 

 peptone " (say 1,000 grams or c.c.) an equal quantity of water, i. e., 

 to make 2,000 grams or c.c. For glycerine broth, add also glycer- 

 ine by volume to make 5% of the total mixture (i. e., 100 c.c.) ; for 

 plain dextrose (or maltose, lactose, etc.) broth, add similarly dex- 

 trose (or maltose, lactose, etc.) to make 1% by weight of the total 

 mixture (i. e., 20 grams). 



