8 MANUAL OF MILK PRODUCTS 



The cells differ when at rest and when active. When at rest 

 the cells lining the alveoli lie flat and close to the wall. Their 

 nuclei are small and spindle form. During a period of activity 

 they are much enlarged, filling nearly the entire cavity, and the 

 nuclei are prominent. The cells may be seen in all stages of 

 reproduction, and in these particulars the gland shows the same 

 characters as seen in the secreting glands already mentioned. 



This theory is further sustained by the antecedents of the 

 milk. When fat is taken into the intestine and assimilated it 

 no longer has an existence as fat, but is broken up into various 

 combinations. Fat as deposited in the body is not the same 

 as the fat in the food. The proportions of olein and stearin 

 have been changed to meet the peculiarity of the animal. 

 Where the analytic and synthetic processes take place is not 

 known. It is now recognized that it is not necessary that the 

 fat in the body be derived from the fat of the food, but that 

 the carbohydrates supply the necessary materials. With these 

 proofs of synthetic' process going on to produce body fat, it is 

 not unreasonable to suppose that a similar process may take 

 place in the formation of milk. 



The milk-sugar, or lactose, is a product of metabolic activity 

 of the protoplasm of the secreting cells of the mammary gland. 

 This particular form of sugar occurs nowhere else in the body. 

 It is a typical carbohydrate, and is found in the milk of animals 

 fed exclusively upon meat, thus showing that the carbohydrates 

 of the food are wholly unnecessary. Of all the constituents, 

 the milk-sugar is least affected by external conditions. 



The casein of milk is thought to be formed the same as the 

 fat, although authorities differ on this point. The evidence 

 seems to be in favor of this theory, for at the beginning and at 

 the end of lactation the albumin, which is normally less than 

 one-seventh of the casein, is actually in excess of it, and albumin 

 is a normal constituent of both blood and milk. The propor- 

 tion of casein in the milk is increased by greater perfection in 



