626 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



that in their functional activity they, to a certain extent, simply modify 

 certain substances already existing in the blood and lymph. 



As regards the production of the fat of milk, oil-globules may be 

 seen to collect in the epithelial cells and escape into the excretory ducts, 

 either by a breaking up of the epithelial cells or by a process of contrac- 

 tion similar to that observed in the amoeba in the process of ejecting 

 the residue from digestion. The origin of the fat is, without doubt, in a 

 process of fatty degeneration of the protoplasmic cell-contents, for the 



cw 



cw 



cw cw 



FIG. 261. DIAGRAM OF THE FORMATION OF THE NIPPLE, AFTER KLAATSH. 



(Ellenberger.) 



I, cat ; II, mare ; III, woman ; IV, cow. DR, milk-cistern ; CW, cutaneous surface. 



amount of fat contained in milk, so far from being increased, is actually 

 diminished by an increase of fat in the food ; while, further, the fats in 

 milk do not necessarily coincide in nature with the fats of the food. On 

 the other hand, an increase in proteid diet increases the amount of fat in 

 the milk. In microscopic examination of the epithelial cells of the 

 mammary glands, oil-globules may be actually seen to increase in size 

 and number until often the protoplasmic contents become almost entirely 



