THE METABOLISM OF THE BODY. 443 
It is, in the nature of the case, impossible to follow with 
the eye the formation and separation of milk-sugar, casein, etc. 
Fie. 336.—I. Acinus from mamma of a bitch when inactive (after Heidenhain). II. During 
secretion of milk. a, b, milk-globules; c, d, e, colostrum-corpuscles 3; J, pale cells. 
But the whole process is plainly the work of the cells, and in 
no mechanical sense a mere deposition of fat, etc., from the 
blood; and the same view applies to the construction of fat by 
connective (adipose) tissue. 
Fig. 337. Fie. 338. 
Fie. 887.—Human milk-globules, from a healthy lying-in woman, eight days after delivery 
(Funke). 
Fie. 338.—Colostrum, from a healthy lying-in woman, twelve hours after delivery (Funke). 
The colostrum-corpuscles are large and granular; they gradually disappear from the 
secretion. 
Whether fat, as such, or fatty acid, is dealt with without 
being built up into the protoplasm of the cell, is not known; 
but, taking all the facts into the account, and considering the 
behavior of cells generally, it seems most natural to regard 
the construction of fat as a sort of secretion or excretion. To 
suppose that a living cell acts upon material in the blood as a 
workman in a factory on his raw material, or even as a chemist 
