82 BACTERIOLOGICAL METHODS 



medium in which prepared casein (nutrose) is the principle in- 

 gredient. Chemically, nutrose is a casemate of sodium and is 

 prepared as follows: Moist casein precipitated from skimmed 

 milk is washed with water in a solution of sodium hydroxide, 

 evaporating the solution to dryness in vacua, powdering the residue 

 and washing successively with alcohol and ether and then dry- 

 ing. It is a coarse, white, odorless and tasteless powder, forming 

 a turbid adhesive solution with water, having an alkaline reac- 

 tion toward litmus and an acid reaction toward phenolphthaleiri. 

 It is a food product intended for the sick because of its easy di- 

 gestion. It is made in Germany but may be secured through any 

 of the larger American pharmaceutical houses (Victor Koechl & 

 Co., New York City). 



The formula for making the artificial milk is as follows: 



Nutrose 24 grams 



Lactose 10 grams 



Distilled water 1000 cc. 



Dissolve the nutrose and lactose in the water (cold) for 

 12 hr. with occasional thorough shaking and then filter 

 through cotton. Tube and sterilize at 110 C. for 20 min., or 

 in the steam sterilizer in the usual manner. No adjustment is 

 required. 



This medium contains all of the nutritive ingredients of cow's 

 milk with the exception of fat which is not desired for the ordinary 

 cultural work. It is of uniform quality and is said to give far 

 more uniform results than cow's milk. It is furthermore more 

 translucent than cow's milk and shows the reactions with in- 

 dicators much better. It would be advisable to make the artificial 

 milk the standard substitute for cow's milk. 



ii. Peptone Medium. This is simply a i per cent, peptone 

 solution in distilled water and is intended to be used for making 

 the indol test. Beef broth from which muscle sugar has been 

 removed by inoculating with B. coli is believed to be objection- 



