HUMAN MILK. 



141 



MILK. 



As already stated, milk is the sole food for the developing 

 child during the early months of its existence, and indeed, as 

 among the Eskimos, for a period extending into years. It is 

 therefore a perfect food, inasmuch as it contains all that is needed 

 for growth and the maintenance of the body in a physiologic con- 

 dition. This is true for the early period of life, but not for the 

 later, as it contains too little iron and too much proteid and fat, 

 although adults have lived for months on milk alone. 



Milk is an emulsion in which the globules of fat are sus- 

 pended in a fluid, called milk-plasma. As in other emulsions, 

 so here, the white color is due to reflection of light from the 

 globules. It is now believed that the fat is not enclosed in a 

 thin envelope of caseinogen, but that by molecular attraction each 

 globule is covered by a closely adherent layer of milk-plasma. 

 The diameter of the globules varies from 0.0015 to 0.05 mm. 



The specific gravity of both cows' and human milk is from 

 1028 to 1034. 



The reaction of milk varies in diiferent classes of animals. 

 In carnivora it is acid, but in most other animals it is either 

 slightly alkaline or neutral. 



Milk contains the following 

 ingredients, the quantity vary- 

 ing in the milk of diiferent ani- 

 mals : Water, caseinogen, lactal- 

 bumin, lactoglobulin, lactose, fat, 

 extractives, as creatin, creatinin, 

 hypoxanthin, cholesterin, and 

 traces of urea, salts, and the 

 gases oxygen, nitrogen, and car- 

 bon anhydrid. 



Human Milk. The first 

 milk secreted by the mammary 



? lands is colostrum (Fig. 86). 

 t is a yellowish liquid, more 

 alkaline than the milk secreted 

 later in lactation, and contains 

 very little caseinogen, sometimes none at all, but lactoglobulin 

 and lactalbumin. Colostrum is regarded by some writers as 

 having a distinct cathartic action on the newborn child ; others 

 deny that it possesses any such power. The following table con- 

 tains analyses by Clemm of human milk before and immediately 

 after delivery : 



FIG. 86. Colostrum and ordinary 

 milk-globules, first day after labor; 

 primipara aged nineteen (after Haskell). 



