MICROSCOPICAL CHARACTERS OF THE MILK 297 



average specific gravity of 1032 is about 1024. The specific gravity of 

 skim-milk is about 1034. 



Microscopical Characters of the Milk. Milk contains a great number 

 of minute spherical globules, of highly refractive power, held in sus- 

 pension in a clear liquid. These are known as milk-globules and are 

 composed of palmitin, olein, fatty matters peculiar to milk, with a little 

 lecithin and sometimes a very small quantity of cholesterin. The 

 globules also contain a small quantity of a yellow lipochrome, or fat- 

 pigment. The specific gravity of pure milk-fat is 949 to 996. 



Human milk-globules are 2T15TO to T2To ^ an ^ ncn ( x to 2O ^) * n 

 diameter. They usually are distinct from each other, but they may 

 occasionally become collected into 

 groups without indicating anything 

 abnormal. In a perfectly normal 

 condition of the glands, when the 

 lacteal secretion has become fully 

 established, the milk contains noth- 

 ing but a clear liquid with these 

 globules in suspension. The pro- 

 portion of fatty matters in milk is 

 twenty-five to thirty-eight parts per 

 thousand ; and this gives an idea of 

 the proportion of globules that are 

 seen on microscopical examination. pig ^,, Human ^ milk . glMes om a 



In SOme regards milk does not healthy lying-in woman eight days after delivery, 

 . , r . . X 400 (Funke). 



present the characters of a simple 



emulsion. When shaken with ether, the mixture remains opaque ; but 

 the fatty matters are dissolved on the addition of potassium hydrate. 

 Dilute acetic acid added to milk causes the globules to run together. 

 These reactions have led to the view that the milk-globules have a 

 membrane that is dissolved by potassium hydrate and by acetic acid. 

 It is probable that the butter in normal milk does not exist precisely in 

 the form of a simple emulsion, but that the globules have a very thin 

 caseous coating. 



In view of the action of various reagents on the milk-globules, the 

 only alternative, if the existence of a caseous coating is denied, is the 

 opinion that the addition of -potassium hydrate or of acetic acid renders 

 the casein incapable of holding the fat in the condition of an emulsion. 

 There is actually, however, little more than a verbal difference between 

 these two opinions. 



Composition of the J/z7/. -- The following table, compiled from 

 analyses by various chemists, gives the constituents of human milk : 



