j 9 o CLEAN MILK 



pasteurized. The tests described on pp. 188-9 ma y tnen be tried to 

 determine positively the presence or absence of preservatives. 



For testing the acidity of milk, an alkali and phenolphthalein 

 are commonly employed. The basis of this test rests on the fact 

 that phenolphthalein turns pink in the presence of an alkali and 

 is colorless in the presence of acid. Therefore in the tests, by 

 adding a known quantity of alkali to a known quantity of milk 

 and phenolphthalein, we may know just how much acidity is present 

 in the milk. For when enough alkali has been added to the milk 

 and phenolphthalein to turn the mixture pink, we know that all 

 the acid in the milk has been neutralized and the mixture is becom- 

 ing alkaline. 



Roughly speaking, increased acidity in milk means increase 

 in number of lactic acid bacilli. The degree of acidity is com- 

 monly tested by health boards in cities to determine the fitness 

 of milk for food. But, as has been recently shown by Bergey, 

 the acid test will not apply to pasteurized milk. There may be 

 hundreds of millions of germs in pasteurized milk without marked 

 acidity. This happens because the germs are not of the acid 

 forming type but belong chiefly to the hay bacillus group (B. sub- 

 tilis). 



These are not usually rated as disease germs, but they make 

 the milk less digestible and nutritious and may produce substances 

 in the milk which cause severe vomiting and diarrhoea in infants. 



By- far the easiest and most convenient method of testing milk 

 or cream for acidity, for those not versed in chemistry, is by means 

 of (Farrington's) alkaline tablets, which may be had of any whole- 

 sale dairy supply company. Milk which contains more than 0.2 % 

 of acid (lactic acid) is not considered sweet, and the acidity of 

 sweet cream varies from 0.15 to 0.2%. The Farrington tablet 

 contains an alkali and phenolphthalein. Two tablets are dissolved 

 in 1 ounce of water and this is added to an ounce of milk. If 

 the mixture remains pink,_theii_the_milk_contains_less than 0.2% 



