

MILK STANDARDS 309 



hydrates, and a small amount of boiled Kubel-Tiemann's litmus 

 solution sufficient to colour the medium a violet tinge. 



(ii) Apply the indole test to each (see Ex. 63). 



(in) Cultivate each in glucose bouillon and determine which 

 gives the Voges-Proskauer reaction (see Ex. 65). 



(iv) Cultivate each kind of organism in plain broth at 37" C, 

 and, after six hours, examine a drop and determine which of 

 them are motile. 



(v) To which species does each belong ; compare the results 

 with the table on p. 306. 



Ex. 148. Determine the relative percentage of liquefying 

 to non-liquefying kinds in several samples of ordinary market 

 milk. 



Dilute the samples to i in 10,000 if twelve hours old; to i in 

 100,000 if twenty-four hours old. 



Inoculate two or three litmus gelatine plates with .5 c.c. of 

 each, and incubate them at 22 C. 



Observe the colonies from day to day ; count the " liquefiers " 

 and "non-liquefiers," and calculate the relative percentage 

 of each. 



Milk containing from 30 to 50 per cent, of liquefying 

 organisms is suspicious and likely to have been contaminated 

 with filth or dirty water. 



Ex. 149. Test the acidity of market samples of milk by 

 the method described in Ex. 134. 



How many fail to reach Newman's standard ? (See p. 311.) 



(TOO c.c. of the milk should not require more than 22 c.c. of 

 decinormal caustic soda solution for neutralization.) 



4. Milk Standards. From time to time various pro- 

 posals have been made, chiefly at the instigation of the 

 medical profession, for the adoption of standards of 

 cleanliness, acidity, and bacteriological characters for 

 all milk supplied to the public. In some countries such 

 standards have been and are more or less rigidly enforced, 



