86 



ESSENTIALS OF CHEMICAL PHYSIOLOGY 



MILK 



Milk is often spoken of as a ' perfect food,' and it is so for infants. 

 Eor those who are older it is so voluminous that unpleasantly large 

 quantities of it would have to be taken in the course of the day to 

 insure the proper supply of nitrogen and carbon. Moreover for adults 

 it is relatively too rich in proteid and fat. It also contains too little 

 iron (Bunge) ; hence children weaned late become anaemic. 



The microscope reveals that it consists of two parts : a clear fluid 

 and a number of minute particles that float in it. These consist of 

 minute oil globules, varying in diameter from 0-0015 to O'OOS milli- 

 metre. 



The milk secreted during the first few days of lactation is called 

 colostrum. It contains very little caseinogen, but large quantities of 

 globulin instead. Microscopically, cells from the acini of the 







6 



Fig. n . — ff, h, colostrum 

 corpuscles with fine 

 and coarse fat globules 

 respectively ; c, d, i\ 

 pale cells flevoid of 

 fat. (HeiJenlialu.) 



Fig. 10. — Microscopic appearance of milk in the 

 early stage of lactation, showing colostrum 

 corpuscles in addition to fat globules. ( Yeo.) 



mammary gland are seen, which contain fat globules in their interior ; 

 thej' are called colostrum corpuscles. 



Reaction and Specific Gravity. — The reaction of fresh cow's milk 

 and of human milk is generally neutral or slightly alkaline. In 

 carnivora the milk is acid. All milk readily turns acid or sour as the 

 result of fermentative change, part of its lactose being transformed 

 into lactic acid (see p. 37). The specific gravity of milk is usually 

 ascertained with the hydrometer. That of normal cow's milk varies 

 from 1028 to 1034. When the milk is skimmed the specific gravity 

 rises, owing to the. removal of the light constituent, the fat, to 1033 to 

 1037. In all cases the spscific gravity of water with which other 

 substances are compared is taken as 1000. 



