100 BOARD OF AGRICULTURE. 



chemical or physiological process which changes the free, fattjr 

 acids produced from starch and sugar into the neutral fats 

 (glycerides, ^. e., combination of the well-known substance, 

 glycerine), than that practical experience disproves the as- 

 sumptions. Physiologists and physiological chemists of to- 

 day recognize almost without exception the important rela- 

 tions which exist between a liberal supply of sugar and starch 

 in the animal diet and the actual accumulation of fat in the 

 animal system ; yet they difl'er more or less as far as their 

 special mode of action is concerned. Some investigator& 

 believe with Liebig, for good scientific reasons, in a direct 

 conversion of sugar and starch into animal fat, leaving the 

 actual proof confidently to future developments. Others 

 deny the actual change of both substances into animal fat ; 

 they ascribe to them merely the functions of protecting the 

 ftit contained in the fodder, and the fat produced from the 

 nitrogenous constituents of the vegetable food whilst passing 

 through the animal system against the oxydizing influence of 

 the air during the process of respiration. (Voit.) 



The beneficial influence of a rich nitrogenous diet on the 

 products of the dairy is frequently mentioned as a substantial 

 proof in that direction. 



All non-nitrogenous constituents of the food, the fat in- 

 cluded, yield to the oxydizing influence of the air and 

 produce the same compounds, namely, carbonic acid and 

 water, whether burned in the open air, or during their circu- 

 lation through the animal body. As they support the 

 process of respiration, Liebig called them the respiratory or 

 heat-producing constituents of the animal food ; he ascribed 

 the entire production of the organic animal heat to a chemi- 

 cal process, and assigned to the non-nitrogenous substances- 

 no other ultimate functions but to produce heat : the amount 

 of carbonic acid and w^ater produced became the direit ex- 

 pression of the consumption of oxygen from the air during 

 the process of respiration. 



These statements are to-day still considered satisfactory in 

 their general application. Chemical reactions are considered 

 the source of animal heat and of animal energy. 



