Kew York Agricultural Experiment Station. 49 



The milk fat could not come wholly fj'ora protein, taking the 

 urine nitrogen to be the measure of the protein broken down, as 

 we necessarily must. Neither could the combined effect of both 

 food fat and decomposed protein account for all the milk fat, 

 the deficit in the case of three cows being large. 



We are now confined to the alternatives of concluding either 

 that previously formed body fat was drawn upon to supply the 

 milk fat or that the carbohydrates were utilized- for this pur- 

 pose. The increased weight of two of the cows, and their gen- 

 erally improved condition during the experiments, preclude the 

 conclusion that 18.4 lbs. and 39 lbs., respectively, of pure fat 

 could have been withdrawn from their bodies. Such a result 

 would have produced a marked change in condition and an 

 appreciable diminution of weight. The case of Cow 2 is 

 especially noteworthy. This was an undersized cow, thin in 

 flesh at the birth of her calf, whose butter fat yield before, 

 during and after the experiment was above 12 lbs. per week, and 

 it did not fall below 10 lbs. for some time, so that her butter 

 production in a year was not less than 500 lbs. During her 

 largest flow of milk at least one-sixth of her fat product could 

 not have been supplied from the normal herd ration she was 

 eating, without drawing upon the carbohydrates. To assume 

 that her small store of previously acquired body fat was drawn 

 upon to the extent of this deficit would be the height of 

 absurdity. Cow 12, eating a fat-poor ration, produced 39 lbs. 

 of milk fat more than the ration could supply independently of 

 the carbohydrates, and to all appearances she could have kept 

 on for a year secreting normal milk from the ration she received. 

 May we not finally conclude, then, that carbohydrates may be a 

 source of milk fat? 



RELATION OF PROTEIN EXCHANGE TO MILK PRODUCTION. 



The relation of protein metabolism to the production of milk 

 is interesting and important. It is recognized, of course, that 



there is a positive demand for protein in the secretion of milk 



« 



solids, and it is not diflicult to calculate the probable extent of 

 4 



