UA-NXJAJj OF CATTLE-FEEDING. 187 



tion of the part played by each, must be left to the deci- 

 feioii of more exact experiments. 



Having thus considered at some length the important 

 quefotion of tlie sources of animal fat> we are prepared to 

 take up the general laws which regulate its formation. It 

 is evident, however, that until we know with certainty the 

 source from whence the fat of the body is derived, our at- 

 tempts to formulate the laws of its production must be 

 more or less tentative. Most of our knowledge upon this 

 subject is due to the labors of Pettenkofer & Voit at Mu- 

 nich. These investigators hold that fat is not formed 

 from carbhydrates in the body, and their experiments, 

 which were made before many of the facts spoken of in 

 the preceding paragraphs were known, are interpreted in 

 accordance with that belief. If we add to this fact the 

 great labor involved in investigations of this kind, the use 

 of the complicated respiration apparatus being essential, 

 w^e can readily understand why our knowledge of the laws 

 of the formation of fat should be in some respects unsatis- 

 factory. At the same time, what is already know n is very 

 valuable and offers important aid to the formation of a 

 rational theory of feeding. 



§ 2. Fbbdino with Fat Alone, 



The Fat of the Food protects the Body-fat. — In 



Pettenkofer & Volt's experiments* a dog was in one 

 case allowed to fast for eight days, and in a second experi- 

 ment was fed daily with 100 grammes of pure fat, about 

 the amount \^^hich was found to have been oxidized daily 

 in the first experiment. On the eighth day the following 

 results were obtained : 



* Zeitschnft f Biologie, V, , 3G9. 



