Origin of Milk Solids 307 



gree to control through feeding or other treatment 

 that is not actual abuse. 



The manner of milk secretion is something of which 

 we know but little, and this is, perhaps, not immedi- 

 ately important to the dairyman. The food source of 

 the constituents of milk is, on the other hand, a mat- 

 ter of great practical interest, and here we have infor- 

 mation more or less definite. 



Sources of milk solids. The previous discussion of 

 the functions of nutrients must have made it clear that 

 the proteids of the milk can have only one source; 

 viz., the proteids of the food, a unanimous conclusion 

 which rests upon experimental evidence as well as 

 upon the universally accepted truth that the animal 

 organism does not have the power to construct pro- 

 teids from simpler compounds. It now seems quite 

 certain that the proteids are the only constituents of 

 milk which must have their origin exclusively in the 

 food proteids, for we have apparently sound reasons 

 for believing that milk sugar and butter fat are con- 

 structed, in part at least, from carbohydrates. In an 

 investigation at the New York Agricultural Experiment 

 Station as to the food sources of milk fat, two cows, 

 both of which gained materially in live weight during 

 experiments continuing two months or over, produced 

 respectively nineteen pounds and forty pounds more of 

 butter -fat than could be accounted for from the food 

 fat and available proteids. The amount of digestible 

 food fat supplied was relatively insignificant and the 

 secretion of milk fat seemed to be related in no direct 

 way to the protein exchange. These observations led 



