New York Agricultural Experiment Station. 519 



There is no way of explaining how milk fat could in any way 

 proceed wholly from metabolized protein in this particular case, 

 but by the improbable theory that the protein joins with other 

 comi>ounds in synthetical changes of which we so far have no 

 hint. 



Certainly, in this experiment, protein metabolism, as ordina- 

 rily understood, can account only for a minor part of the fat 

 secreted in the milk, because without the aid of other compounds 

 protein must form considerably less than its weight of fat. Some 

 nitrogen compound must be split off which would take part of 

 the carbon and hydrogen with it. 



The only rational conclusion which these data seem to offer is 

 that the milk fat, as previous experiments have demonstrated to 

 be the case with body fat, was produced, in part at least, from 

 carbohydrates. Such data do not constitute evidence that pro- 

 tein or food fats may not under other conditions be the source of 

 milk fat, but only that in this experiment they were an utterly 

 insufficient source, either directly or indirectly. 



The Stimulus of Protein upon Milk Production. 



If further investigations, which are now planned for the inmne- 

 diate future, should ratify the apparent outcome of this one, the 

 explanation of the well-known stimulus of an abundant supply of 

 protein upon milk secretion must rest upon some other basis than 

 that so much protein is necessary as a source of milk building 

 material. It is generally held, from the standpoint of both sci- 

 ence and practice, that considerably over two pounds of digesti- 

 ble protein, two and one-half pounds being the amount agreed 

 upon, should be fed in connection with a sufficient supply of car- 

 bohydrates (12| lbs.) to a cow in the full flow of milk, if a maxi- 

 mum food efficiency is to be attained. 



Experiments have shown that the food efficiency of a unit of 

 digestible matter is actually augmented by increasing the pro- 

 portion of protein up to approximately the quantity named, as 

 for instance when oil meal or gluten meal is substituted for a 

 portion of the cereal grains in a ration otherwise made up wholly 

 of home grown foods. Surely if protein takes no necessary part, 



