10 



NATURE AND COMPOSITION OF MILK. 



The proteids of milk consist largely of casein. 

 There is also some albumin (the form called lactal- 

 bumin) from .035 to .050 per cent, being usually- 

 present, together with traces of globulin. The albumin 

 is coagulated by boiling. The condition in which the 

 casein exists is still obscure, but the results of recent 

 investigation render it probable that it is in combina- 

 tion with the calcium phosphate. Acids break up this 

 combination, and precipitate the casein in an insoluble 

 form. Heat alone does not produce this effect. The 

 form in which the casein exists prior to coagulation is 

 now frequently called " caseinogen ". 



Citric acid is a normal constituent of the milk of 

 various animals. In human milk, the quantity is about 

 0.5 gram to the liter, in cow's milk from i to 1.5 

 grams. It is not dependent on the citric acid present 

 in the food. 



Minute amounts of nitrogenous bases and a starch 

 converting enzyme also occur. 



