174 NUTRITION OF FARM ANIMALS 



vocate the belief that protein constitutes an important source 

 of animal fat, this conclusion being based largely on the famous 

 respiration experiments of Pettenkofer and Voit at Munich in 

 which a dog was fed lean meat freed from visible fat as carefully 

 as possible (this being the nearest practicable approach to a 

 pure protein diet) and the balance of nitrogen and carbon 

 (287, 292) determined. The results showed in many cases a 

 retention of carbon by the animal greater than corresponded to 

 the quantity of protein gained, and this difference was inter- 

 preted, according to the methods described in Chapter VI 

 (293), as showing a production of fat. 



Pettenkofer and Volt's experiments were long accepted as 

 conclusive until Pflliger l subjected them to destructive criti- 

 cism, showing the possibility of material errors in the estimates 

 of the carbon of both feed and visible excreta. 



It scarcely need be said that this result does not prove that 

 fat is not formed from protein, but simply that Pettenkofer and 

 Voit's experiments fail to demonstrate it. Of later experi- 

 ments on the subject, a number seem to show clearly the for- 

 mation of a small amount of fat from protein, even after every 

 allowance has been made for the objections raised by Pfliiger 

 in his criticisms of the experiments. A number of negative 

 results have, it is true, also been reported, but naturally nega- 

 tive results are of much less value than positive ones. 



Moreover, the indirect evidence in favor of the possibility 

 of the formation of fat from protein seems practically conclu- 

 sive. As already stated (235), it has been established beyond 

 reasonable doubt that carbohydrates may be produced from 

 protein in the body. If this is true, however, it almost neces- 

 sarily involves the possibility of the formation of fats from pro- 

 tein, since carbohydrates are undoubtedly a source of fat. 



249. Fat from carbohydrates. Pettenkofer and Voit, 2 how- 

 ever, went further than to demonstrate, as they believed, the 

 formation of fat from protein. Their experiments included a 

 number in which carbohydrates were added to a ration of 

 protein (lean meat). Assuming with Henneberg 3 that 100 

 grams of protein might yield 51.4 grams of fat, they computed 

 that all the fat produced by the animal in these experiments 



1 Arch. Physiol. (Pfluger), 51 (1892), 229. 



2 Ztschr. Biol., 9 (1873), 435. 3 Lanclw. Vers. Slat.., 10 (1868), 455. 



