88 



PHYSIOLOGY. 



to the top, constituting the cream ; this includes also a considerable 

 amount of caseine, with the sugar and salts of the milk. By agitating 

 the cream the envelopes of the oil-globules are ruptured, and it is 

 separated into butter and butter-7tiilk^ the latter containing the caseine^ 

 sugar, &c. A small quantity of caseine, however, is generally en- 

 tangled with the butter, which has a tendency to render it rancid, 

 and should be removed by heat. 



After the removal of the cream the milk still contains the greatest 

 part of the caseine and sugar ; if kept long enough the sugar is con- 

 verted into lactic acid, which coagulates the caseine, precipitating it 

 in small flakes. The same precipitation may be accomplished by 

 other acids ; the most effectual is that contained in the rennet, or 

 dried calf's stomach, the active principle of which will coagulate 

 30,000 times its weight of milk. The sugar may be obtained by 

 evaporating the whey. 



The proportion of the solid ingredients of the milk is about 110 

 parts in 1000, varying according to constitution, the amount and 

 character of ingesta, and the time which has elapsed sinceparturition. 



The first milk is called the Protogala, or Colostrum, and has a 

 purgative effect upon the child, owing to the presence in it of numer- 

 ous yellow granulated corpuscles, called colostrum corpuscles. This 

 property soon disappears, however, though occasionally it returns 

 after the expiration of twelve months, seeming to indicate that the 

 flow should be no longer encouraged. 



Human milk contains more sugar and less caseine than that of the 

 cow, a fact to be remembered in substituting the latter for the former. 

 The milk of carnivorous animals, fed exclusively on animal diet, con- 

 tains scarcely a trace of sugar, while the caseine and butter are 

 abundant. 



The quantity of milk that can be squeezed from either breast at 

 one time is about two ounces. It is not always the largest breasts 

 that secrete most milk, since their great size is often owing to 

 the presence of adipose matter. The secretion is often materially 

 affected by emotions, &;c., so as to become poisonous to the child ; 

 and it is often rendered medicinal by substances administered to the 

 mother. 



The instances of vicarious secretion of milk are not numerous; 

 and in no instance is there any proof that the elements of the fluid 

 were pre-existent in the blood. The secretion sometimes occurs in 

 undoubted virgins, widows, and women past the child-bearing period, 

 as well as in males. 



Secretion of Bile. — The Liver is perhaps more universally pre- 

 sent throughout the animal scale than any other gland. It is the 

 largest gland in the body, weighing from three to four pounds. The 

 entire organ is made up of a vast number of minute lobules, of irre- 

 gular form, of about the average size of a millet seed. Each of these 



