MILK SECRETION 5 



in order to determine what became of the food the cow con- 

 sumed. Their conclusions are as follows : 



"A cow fed during ninety-five days on a ration from which 

 the fats had been nearly all extracted, continued to secrete 

 milk similar to that produced when fed on the same kinds of 

 hay and grain in their normal condition. 



"The yield of milk-fat during the ninety-five days was 62.9 

 lb. The food fat eaten during this time was 11.6 lb., 5.7 lb. 

 only of which was digested, consequently at least 57.2 lb. of 

 the milk-fat must have had some source other than the food 

 fat. 



"The milk-fat could not have come from previously stored 

 body fat. This assertion is supported by three considerations : 

 (1) The cow's body could have contained scarcely more than 

 60 lb. of fat at the beginning of the experiment ; (2) she gained 

 47 pounds in body weight during this period of time with no 

 increase of body nitrogen, and was judged to be a much fatter 

 cow at the end ; (3) the formation of this quantity of milk-fat 

 from the body fat would have caused a marked condition of 

 emaciation, which, because of an increase in the body weight, 

 would have required the improbable increase in the body of 

 104 lb. of water and intestinal contents. 



"During fifty-nine consecutive days 38.8 lb. of milk-fat was 

 secreted and the urine nitrogen was equivalent to 33.3 lb. of 

 protein. According to any accepted method of interpretation 

 not over 17 lb. of fat could have been produced from this 

 amount of metabolized protein. 



"The quantity of milk solids secreted bore a definite relation 

 neither to the digestible protein eaten nor to the extent of the 

 protein metabolism. 



" The composition of the milk bore no definite relation to the 

 amount and kind of food. 



"The changes in the proportion of milk solids were due almost 

 wholly to changes in the percentage of fat." 



