Milk Sugar and Ash 25 



The sugar. — Milk sugar, otherwise called lactose, 

 exists in solution in the milk serum. It has the 

 same chemical composition as cane sugar : that is, 

 C12H22O11 -|- H2O. It crystallizes with considerable 

 difficulty, and has very much less sweetening power 

 than ordinary sugar. Under the influence of vari- 

 ous ferments it readily undergoes decomposition, 

 each molecule of sugar breaking up into four mol- 

 ecules of lactic acid. This change begins in the 

 milk almost immediately after it is drawn, and con- 

 tinues until about .8 of 1 per cent of lactic acid 

 is formed. The presence of lactic acid in this 

 amount acts as a check upon the growth of the 

 ferments, and prevents the further formation of 

 lactic acid, unless the acid is neutralized with an 

 alkali, when the fermentation proceeds as before. 

 Milk sugar does not readily undergo alcoholic fer- 

 mentation, but by the action of yeast and some 

 other ferments the lactose is "inverted," or changed 

 to dextrose and a peculiar substance known as ga- 

 lactose, and these readily change to alcohol under 

 the influence of the proper ferments. 



The ash. — The ash is the smallest and least 

 variable constituent of the milk. It is composed 

 chiefly of the phosphates of lime and potash, the 

 chlorides of potash and soda, with small amounts 

 of phosphate of iron and magnesia. Most of the 

 salts are in solution. It seems probable that at 

 least a part of the phosphate of lime is ordinarily 

 in insoluble form, suspended in the milk in very 

 fine particles in connection with the casein. The 



