Xew York Agricui.ti ual Exteriment Station. 517 



The Food Fats and Body Fats as Sources of the Milk Fats. 



The results of this experiment appear to demonstrate conclu- 

 sivelv that food fats bear no necessary relation to the formation 

 of milk fats. 



In the ninetj-five days that this cow ate rations from which 

 the fats were largely extracted, she produced 62.9 lbs. of milk 

 fat. The quantity of fats in the food during the same time was 

 11.6 lbs., only 5.7 lbs. of which was digested, leaving 57.2 lbs. of 

 milk fats in excess of the food fat supply. It is very clear that 

 the milk fats were not taken as such from each day's rations. 

 Could they not have come from the body fat already deposited in 

 the animal when the experiment began? This is so highly im- 

 probable as to justify a positive negative answer. At the begin- 

 ning of the ninety-five days the cow weighed 867 lbs. She was 

 quite lean and certainly could have been no fatter than the well- 

 fed ox which Lawes and Gilbert found to contain 7.1 per cent of 

 fat. The total fat in her body could, therefore, scarcely have 

 exceeded 61 lbs., and was probably less. Practically all of this 

 possible maximum would have been required to produce the 57.2 

 lbs. of milk fat and it is not reasonable to suppose that the cow 

 lost all her body fat when we see that during the period under 

 consideration she gained 47 lbs. in live weight. There could not 

 have been a large increase of flesh, for during 59 days of this 

 period the nitrogen income and outgo were about evenly 

 balanced. 



It may be suggested that a change in the water of the body 

 and in the contents of the intestines might cause large variations 

 in body weight, which would obscure a loss of body fat. In this 

 case, however, such a criticism would not be rational. Not only 

 must 57.3 lbs. of fat be replaced by water or an intestinal food 

 residue but an addition to the body weight of 47 lbs. must be 

 accounted for in the same way, a total of 104 lbs. Such a result 

 would Ixave necessitated a very marked condition of emaciation 

 and a noticeably full condition of the intestinal tract, the reverse 

 of which was true. As before stated the cow apparently grew fat 

 steadily during a large part of the experiment. We are therefore 



