MILK SECRETION 27 
down process is completed, the transformed cells appear at 
the opening of the alveoli in the form of distinct fat-globules. 
This is supposed to be the origin and formation of fat-globules 
in milk; so it may be said that so far as known the fat 
is the result of a breaking down of degenerated epithelial cells. 
Dr. Bitting asserts that the formation of milk solids in the 
cow’s udder is probably due to a metabolic process rather than 
a a 
Fie. 3.—A schematic figure showing the course of the artery leading to the 
mammary g:and and the veins returning to the heart. The light-colored 
lines represent arteries and the dark-colored lines the veins. (From 
Bitting, Twelfth An. Report, Indiana.) 
to a degenerative. Collier found that a cow giving a normal 
amount of milk would secrete about 136,000,000 fat-globules 
per second. He also suggests that a cow secretes about 5 
pounds of milk solids per day. As a cow’s udder weighs only 
about 24 pounds, the whole udder would have to be renewed 
twice daily. This is not consistent with our present knowledge 
of tissue building. 
