THEORETICAL CONSIDERATIONS. 29 



milk secreted, there takes place little by little, a sort of granu- 

 lation, and finally the cells fill with fat. These latter constitute 

 the milk globules surrounded by casein; they are suspended in 

 a liquid containing casein, milk sugar, and various salts. Milk, 

 as previously pointed out, is in reality a sort of fatty degenera- 

 tion of the cells of the milk glands; in other words the nitrogen- 

 ous elements of w^hich they consist are transformed into milk 

 as soon as the glands enter into activity. Casein does not exist 

 ready formed in the blood, but depends upon the association 

 of certain cells. This explains why the colostrum does not 

 contain it just before the calf is born. Milk sugars appear to 

 be the result of the decomposition of albumin and fat. 



Milk has, all facts considered, a very regular composition. 

 Just what effect nervous excitement produces remains an open 

 question. The quantity and quality of milk are determined 

 mainly by the composition and size of the milk glands. A well 

 known fact is that with the same fodder the volume of milk ob- 

 tained from different cows will vary considerably. Wolff calls 

 attention to the fact that the cows belonging to the mountains 

 will give a richer milk than those of the valleys; that very 

 young cows will give less milk than older ones. 



It is impossible, even by careful feeding, to bring about a 

 satisfactory secretion of milk, unless the milk glands are con- 

 stituted for its formation. In this question the race and indi- 

 vidual characteristics play a part. Under these conditions the 

 abnormal development of the udder is not a sure indication in 

 advance of the possibility of an abundant flow of milk. Con- 

 sequently, while feeding is very important, it is not the most 

 essential requisite, and although it has a considerable influence 

 upon the volume of milk obtained, it has very little upon its 

 composition. Above all, the introduction of considerable 

 protein is important, as upon it the constant renewal of the 

 cells of the milk glands depends, as these cells are not only 

 made up of protein, but are filled with it. Another fact is that 

 albumin appears to increase the percentage of solid matter con- 

 tained in milk. It is important that the protein reach the milk 

 glands as promptly as possible, hence the albumin must be of 

 the circulatory order. 



