MAI^UAL OF CATTLTS-FEEBING. 105 



quires for its complete combustion one gramme of oxygen, 

 the same weigiit of fat will require 2.5 grammes of oxygen ; 

 and if we represent the respiration equivalent of starcli by 

 1, that of fat is 2.5, while that of the other carbhydrales 

 is practically equal to that of starcli, viz., 1. 



Since, now, the chief office of the carbhydrates seems 

 to be to protect other substances from oxidation by them- 

 selves combining with the ovygen, we might naturally ex- 

 pect that one part of fat would be equivalent in this respect 

 to 2.5 parts of a carbhydrate ; and before any exact obser- 

 vations had been made, this was assumed to be the case. 

 The few experiments as yet made, however, have shown 

 that this assumption is erroneous, and that one part of fat 

 is equivalent not to 2.5 parts of a carbhydrate, but to only 

 about 1.75 parts, while, as we have seen (p. 157), their 

 action in decreasing the protein consumption is about the 

 same, weight for weight. In the animal body we have to 

 do, not with a machine into which fuel is put to be burned, 

 but with a living organism. The materials of the body 

 and the food are decomposed in the performance of the 

 vital processes, while the burning of them by the oxygen 

 of the blood is only a secondary process, and. any conclu- 

 sions drawn from the chemical composition of nutrients 

 and their behavior outside the body, are of very uncertain 

 application to the complicated processes which take place 

 within it. 



The importance of these facts for the practice of feed- 

 ing is obvious. The carbhydrates are the cheapest of the 

 nutrients, and the most easily digestible, while fat is ex- 

 pensive and diflScult of digestion by herbivorous animals. 

 "When we add to the two facts just mentioned — viz., the 

 equivalence of fat and carbhydrates in their effect on flesh 

 production, and the value of the latter as an aid to fat pro- 



