MILK PRODUCTION 467 



It should perhaps be pointed out that the formation of fat from 

 carbohydrates in these experiments may not necessarily have occurred 

 in the milk gland itself. It is entirely conceivable that the main 

 portion of the synthesis of the fat may have taken place elsewhere 

 and that the fat or its precursors were simply transferred to the milk 

 gland. 



Second, it has also been shown by a considerable number of 

 experiments that, as in the case of body fat, the fat of the feed 

 may sensibly affect the properties of the milk fat. Not only 

 have changes in the melting point, iodin number, and other 

 properties of butter fat been found to follow in a general way 

 similar changes in the feed fat, but characteristic ingredients 

 of foreign fats given in the feed have been detected in the milk. 

 While it is not necessary to conclude, and is indeed unlikely, 

 that the feed fat is simply transferred, as it were mechanically, 

 to the milk, it is clear, on the other hand, that relatively large 

 fragments of the fat molecule are able to pass through the 

 epithelial cells into the milk. These facts render it evident 

 that feed fat is a source of milk fat. Not only so, but experi- 

 ments by Morgen and his associates, to be mentioned later (613), 

 seem to show that a certain amount of fat in the feed (in her- 

 bivorous animals at least) conduces to the most efficient pro- 

 duction of milk fat. 



The idea that the fat of milk is produced synthetically to a 

 considerable extent is perhaps supported also by the presence 

 in it of the lower acids of the aliphatic series, which may be 

 intermediate steps in the synthesis of fat from simpler carbon 

 compounds, or, on the other hand, may arise during the partial 

 breaking up of the carbon chain in the feed fat which probably 

 precedes its transformation into milk fat. 



As a general conclusion, therefore, it may be stated that the 

 fat of milk may have its origin either in the fat or in the carbo- 

 hydrates of the feed, or in both. Whether it may also be pro- 

 duced from protein has not been demonstrated experimentally, 

 but reasoning by analogy with the formation of body fat, it 

 must be regarded as at least very probable. 



554. Origin of lactose. The lactose of milk is a disaccharid 

 yielding upon hydration dextrose and galactose. Dextrose or 

 its derivatives are abundant in the feed of herbivorous animals 

 and it is also a constant ingredient of the blood. On the other 



