8 VOELCKER on the Chemistry of Food. 



gous if not identical with the several kinds of fat which form 

 part of the bodies of animals. The fatty matters of food, without 

 undergoing much change, are therefore readily assimilated by 

 the animal organism, and applied when given in excess to the 

 storing up of animal fat Vegetable oils and fats, given along 

 with a scanty supply of starchy food, are used to support respira- 

 tion ; and, on the other hand, starch, gum, and sugar, when given 

 to fattening beasts in excess, are transformed into animal fat. 

 There is thus no essential difference in the fatty or the starchy 

 constituents of food, in so far as their use is concerned. According 

 to circumstances, vegetable fatty matters are either stored up in 

 the animal system or employed to support respiration ; on the 

 other hand, starch or sugar, which are usually employed to feed 

 the respiration, are, under favourable conditions, changed into 

 animal fat. The proportion of carbon in fatty matters amounts 

 to about 80 per cent., and is much larger than in starch or 

 sugar. On account of this deficiency in carbon the latter com- 

 pounds are not so well adapted for the laying on of fat. On the 

 other hand, all food containing much ready made fat or oil is justly 

 esteemed for fattening beasts. The changes which starch, sugar, 

 gum, and similarly constituted substances undergo in the animal 

 system are readily explained. These compounds consist of 

 carbon and water only, and on account of the simplicity of their 

 composition are well adapted to feed the respiration. In breathing, 

 the atmospheric air taken in by the lungs supplies the oxygen, 

 which, combining with the carbon of starch or sugar, produces 

 carbonic acid in abundance, which is thrown off with watery 

 vapours in exhaling. The quantity of carbon consumed during 

 respiration of animals varies at different times, in different 

 species, according to rapidity of breathing and mode of living. 

 Under all circumstances, however, it is considerable. Thus a 

 horse, according to Boussingault, throws off daily 45 Ibs. of carbon 

 in the form of carbonic acid gas ; and in the case of the cow four- 

 ninths of the carbon contained in the daily food is consumed 

 during the process of respiration. Animals therefore require 

 food not merely to support or to increase the weight of their 

 bodies, but also to furnish the necessary amount of carbon re- 

 quired for supporting respiration. When starch or sugar is 

 burnt in the air, the oxygen of the latter unites with the carbon of 

 the former, and both together are dissipated in the form of 

 carbonic acid, with the production of much heat. The process of 

 respiration resembles intimately the act of combustion. It is in 

 fact a slow combustion, and, like all processes of that descrip- 

 tion, is attended with evolution of heat. The amount of heat 

 thus generated is proportionate to the quantity of carbon con- 



