78 MILK 



The results of Jordan and Jenter's experiment appear to dem- 

 onstrate that food fats bear no necessary relation to formation 

 of milk-fat. Protein metaboHsm can account only for part of 

 the fat secreted in the milk, and some of the fat must have been 

 derived from carbohydrates. 



The assumption appears to be justified that milk-fat is derived 

 from four sources, namely, food-fat, body fat, protein, and car- 

 bohydrate. It is the function of the milk glands to transform 

 these substances into milk-fat, and they produce a fat which varies 

 but little from a standard suitable for the food of a certain species. 

 It is true that the chemical composition of milk-fat in the same 

 kind of milk varies within limits, according to the kind of fat 

 contained in the food consumed. However, such variations are 

 not permanent, and after a short period the normal constitution 

 of the fat is restored, even when a particular fat is eaten with the 

 food for a long time. 



Milk-sugar occurs naturally only in milk and in the urine of 

 maminals at the commencement and after the close of lactation. 

 If the mammary gland is extirpated, milk-sugar disappears from 

 the urine, which fact leads to the conclusion that the milk glands 

 are the exclusive sources of milk-sugar. 



At present the most generally accepted view is that milk- 

 sugar is derived from dextrose in the circulation. Specific action 

 of the milk glands transforms dextrose into lactose. When the 

 mammary glands are extirpated dextrose appears in the urine, 

 but if they are not completely removed lactose appears in the urine. 

 Furthermore, injection of dextrose into lactating animals leads to 

 the appearance of lactose in the urine. There can, therefore, be 

 no doubt about the origin of lactose from dextrose, the latter 

 being transformed into the former in the milk glands. 



Mineral Constituents. — Fleischmann thinks that the origin of 

 the salts in milk must be looked for in the mammary glands. The 

 composition of milk ash differs from that of the blood and lymph 

 of the cow, and therefore it cannot be assumed that mineral mat- 

 ter passes unaltered through the mammary gland. Feeding of 

 phosphates has not been known to increase the phosphorus con- 

 tent of milk. The water in milk probably comes directly from the 

 blood and lymph, and carries with it in solution some mineral 

 matter and also some organic substances, such as m-ea and hypo- 

 xanthin. 



The Chemistry op Butter-fat 



Milk-fat is a compound of triglycerids, cholesterin, and a 

 pigment. It is not a simple mixture of triglycerids; it is rather a 

 chemical compound — a fact which can be proved by several 



