Animal NutrUion. 59 



Even Avhen the food given consisted of non-nitrogenous mate- 

 rials only, there was a laying-on of fat; when only protein was 

 fed, the excretion of urea was increased proportionately, and there 

 -vas a small production of fat, which may have been derived from 

 the small amount of fat always present in lean meat. 



Voit found from a number of experiments that carbohydrates 

 ■ cause a decrease of fat consumption in the body, and that they 

 are oxidized in preference to the body fat. If enough carbohy- 

 drates are fed with the protein, all the fat that may have origi- 

 nated from the protein may be deposited as body fat. If the 

 quantity of carbohydrates fed is increased beyond this point, 

 there will be no fui-ther laying-on of fat, the excess of carbohy- 

 drates being burned. In this particular the carbohydrates act 

 differently from fat fed in conjunction with protein, since the 

 more fat the animal can be induced to eat the larger will be the 

 quantity of fat deposited. 



Voit's position, that even the largest quantities of carbohydrates 

 fed in connection with protein are decomposed in the animal 

 body, is held untenable by Pfl tiger, 1 who maintains that if an 

 amount of fat or starch above the needs of the system be fed to 

 an animal whose nitrogen income and outgo has been brought to 

 a state of equilibrium, the nutritive balance will not be imauenced 

 thereby; i. e., the excretion of urea and oxidation of carbon wiU 

 go on without increase, the excess of fat or starch passing off 

 undigested. 



84. Relative value of fat and carbohydrates.— In experimenta 

 with fat and carbohydrates for fat production in the animal body, 

 Pettenkofer and Voit* found that 100 parts of fat were equivalent 

 to 172-179 parts, average 175 parts, of carbohydrates (starch) 

 for this pui-pose. When considering the formation of flesh in the 

 animal body, it was shown that carbohydrates and fat were 

 practically of equal value, pound for pound, as aids in flesh for- 

 mation. (70) Neither of these offices can be filled by fats to the 

 extent indicated by their fuel value as determined by calorimetric 

 investigations, (60) or as would be inferred from the quantity of 



1 Pfluger's Archiv, 51 (1892), p. 317. 

 * Voit, Physiologie, p. 150. 



