Composition of Milk and Its Products. 17 



Ordinarily the souring of milk is, however, more 

 complicated, and other organic bodies, like butyric acid, 

 alcohol, etc., and gases like carbonic acid are formed, 

 resulting in a loss in the feeding value of the milk. 

 While sour milk may therefore contain a somewhat 

 smaller proportion of food elements than sweet milk, the 

 feeding of it to farm animals, especially pigs, will gen- 

 erally produce better results than is obtained in feeding 

 similar milk in a sweet condition. The cause of this may 

 lie in the stimulating effect of the lactic acid of sour 

 milk on the appetites of the animals, or in its aiding 

 digestion by increasing the acidity of the stomach juices. 



That the souring of milk is due to the activities of 

 bacteria present therein is shown clearly by the fact that 

 sterile milk, i. e., milk in which all germ life has been 

 killed, will remain sweet for any length of time when 

 kept free from infection. 



The amount of milk sugar found in normal cows' milk 

 varies from 3.5 to 6 per cent., the average content being 

 about 5 per cent. ; in sour milk this content is decreased 

 to toward 4 per cent. 



20. Ash. The ash or mineral substances of milk are 

 largely composed of chlorids and phosphates of sodium, 

 potassium, magnesium and calcium; iron oxid and sul- 

 furic and citric acids are also present in small quantities 

 among the normal mineral milk constituents. The 

 amount of the different bases and acids found in milk 

 ash have been determined by a number of chemists; the 

 average figures obtained are given in the following table, 

 calculated per 100 parts of milk (containing .75 per 



cent of ash) and per 100 parts of milk ash. 

 2 



