176 NUTRITION OF FARM ANIMALS 



the feed. This was particularly the case as it came to be more 

 clearly recognized that Henneberg's estimate of a production 

 of 51.4 grams of fat from 100 grams of protein was in all prob- 

 ability too high, and especially after it was shown that what 

 had been regarded as digested protein in many of these experi- 

 ments (i.e., digestible N X 6.25) consisted in part of much 

 simpler nitrogenous compounds. The ready formation of 

 fat by the hog rendered this animal a very suitable subject for 

 experiment, and the great majority of investigations on this 

 animal have supported the view that fat is produced from 

 carbohydrates, but similar results upon other species have not 

 been lacking, while respiration experiments upon swine, geese, 

 dogs, and especially the extensive investigations by G. Klihn l 

 upon cattle have completed the demonstration. 2 



In the light of all these results, the formation of fat from 

 carbohydrates in the animal body is now universally admitted, 

 while its production from protein is still questioned by a few 

 and in any case is of little economic significance, so that we 

 have come back by a curious reversal of views almost to Lie- 

 big's classification of the nutrients into plastic and respiratory. 



This conclusion applies specifically to the pure hexose carbo- 

 hydrates, particularly starch. In many of the experiments 

 cited, however, the non-nitrogenous material digested by the 

 animal consisted to a not inconsiderable extent of those sub- 

 stances of uncertain chemical nature included in the terms 

 crude fiber and nitrogen-free extract. Postponing for the 

 present any discussion of the nutritive value of these groups, 

 it may suffice to say here that Kellner's investigations 3 in 

 particular show that both of them, including the pentosans, may 

 serve as sources of fat. 



Katabolism 



250. Body fat a reserve. The stored fat of the adipose tis- 

 sues, aside from its mechanical functions, constitutes the great 

 reserve of energy-yielding material in the body. In the lack of 

 an adequate feed supply, common observation shows that this 



1 Kellner : Landw. Vers. Stat. ; 44 (1894), 257. 



2 Compare the author's Principles of Animal Nutrition, pp. 165-184. 

 3 Landw. Vers. Stat.; 51 (1900). 



