SECRETION. 



smaller in size than in the colostrum ; as the largest of them are 

 not over 2uVo f an i nc ^ i n diameter, and the greater number 

 about yeiffTj of an inch. 



The following is the composition of the butter of cow's milk, 

 according to Robin and Yerdeil : 



Margarine .......... 68 



Oleine 30 



Butyrine .......... 2 



100 



It is the last of these ingredients, the butyrine, which gives the 

 peculiar flavor to the butter of milk. 



The milk-globules have sometimes been described as if each one 

 were separately covered with a thin layer of coagulated casein or 

 albumen. No such investing membrane, however, is to be seen. 

 The milk-globules are simply small masses of semi-fluid fat, sus- 

 pended by admixture in the watery and serous portions of the 

 secretion, so as to make an opaque, whitish emulsion. They do 

 not fuse together when they come in contact under the microscope, 

 simply because they are not quite fluid, but contain a large pro- 

 portion of margarine, which is solid at ordinary temperatures of the 

 body, and is only retained in a partially fluid form by the oleine 

 with which it is associated. The globules may be made to fuse with 

 each other, however, by simply heating the milk and subjecting it 

 to gentle pressure between two slips of glass. 



When fresh milk is allowed to remain at rest for twelve to twenty- 

 four hours, a large portion of its fatty matters rise to the surface, 

 and form there a dense and rich-looking yellowish-white layer, the 

 cream, which may be removed, leaving the remainder still opaline, 

 but less opaque than before. At the end of thirty-six to forty-eight 

 hours, if the weather be warm, the casein begins to take on a 

 putrefactive change. In this condition it exerts a catalytic action 

 upon the other ingredients of the milk, and particularly upon the 

 sugar. A pure watery solution of milk-sugar (C 24 H 24 O 24 ) may be 

 kept for an indefinite length of time, at ordinary temperatures, 

 without undergoing any change. But if kept in contact with the 

 partially altered casein, it suffers a catalytic transformation, and is 

 converted into lactic acid (C 6 H 6 O fi ). This unites with the free soda, 

 and decomposes the alkaline carbonates, forming lactates of soda 

 and potassa. After the neutralization of these substances has been 

 accomplished, the milk loses its alkaline reaction and begins to turn 

 sour. The free lactic acid then coagulates the casein, and the milk 



