CHAPTER XII 



MILK AND ITS PRODUCTS. 



Milk is a valuable agricultural product and both it and the 

 products obtained from it are of considerable commercial and in- 

 dustrial importance. The dairy products of the State of Wis- 

 consin alone are valued at $75,000,000. 



Secretion. Milk is the secretion of special glands in the mam- 

 malian female and adapted to the nourishment of the newly born 

 young of that particular species. The constituents of the milk 

 are especially elaborated by the cells of the mamma; these con- 

 stituents do not exist preformed in the blood, but are formed by 

 profound chemical processes, little understood, out of the nu- 

 trients carried in the blood to the active cells. For example, no 

 casein or milk sugar exists either in the food of the cow or in her 

 blood, but from the nitrogenous constituents of blood, the com- 

 plex protein, casein, is elaborated ; also, from the simple sugar 

 dextrose, the more complex milk sugar is formed. This is all 

 accomplished through the wonderful activities of the udder cells. 

 That the composition of the milk is closely related to the food re- 

 quirements of the newly born young and its rate of growth, has 

 been suggested by the physiologist, Bunge. This relates partic- 

 ularly to the ash and protein materials of milk, which are so 

 necessary for the life processes and the rapid building of the 

 growing young. 



The following table will clearly show that the ash of milk and 

 of the new born young are very much alike, while they have an 

 entirely different composition from the fluid out of which they 

 are formed, namely the blood, and especially the blood serum; 

 from a consideration of such facts, it appears certain that the 

 cells of the milk gland must possess the power of selection and 

 that milk is not merely filtered from the blood. 



