828 NUTRITION AND HEAT REGULATION. 



from the fat of the food. Liebig, applying his more exact methods, 

 demonstrated that in some cases at least this source is insufficient 

 to account for all the fat. The fat yielded by the milk of a cow 

 for instance, may be greater in quantity than the fat contained 

 in the food. He also pointed out that the fat of each species of 

 animal is more or less peculiar, the fat of the sheep having a higher 

 melting point than pork fat, and both differing in composition from 

 the fat taken as food. "In hay or the other fodder of oxen no 

 beef suet exists, and no hog's lard can be found in the potato refuse 

 given to swine." He was led to attribute the source of body fat 

 chiefly to the carbohydrate food, and this belief agreed well with 

 the experience of agriculturists as to the use of such foods in fatten- 

 ing animals for market. This view, in turn, was displaced by the 

 theory of Voit, supported by elaborate feeding experiments. Voit 

 believed that the fat of the body is formed mainly or entirely from 

 the protein of the food, the carbohydrate and the fat of the diet 

 being useful only to protect a part of this protein from oxidation. 

 Voit's experiments have been shown by Pfliiger to have been based 

 upon erroneous analyses of the meat used in his experiments. Voit 

 assumed that in this meat the ratio -Q- is equal to 1.34 to 1.37, while 

 Pfliiger showed that it is lower,* 1.33. The modern point of view 

 is that the fat of the body originates partly from the fat of the food, 

 particularly in carnivora, and partly from the carbohydrate of the 

 food, especially in herbivora, in whose diet this foodstuff forms 

 such a large part. Whether under any circumstances the pro- 

 tein food may also serve as a source of body fat is still an open 

 question, decisive experiments being lacking. 



Origin of Body Fat from Food Fat. The first proofs that 

 the food fats may be deposited as such in the fat tissues of the 

 body were obtained by feeding foreign fats to dogs and demon- 

 strating that these fats can afterward be recognized in the 

 tissues of the animals, t Linseed oil, rape-seed oil, and mutton-fat 

 were used in these experiments. Secondly, it has been made 

 probable by feeding experiments that the normal fat of the food 

 undergoes a similar fate. Thus, Hofmann used a dog weighing 

 26 kgms. and allowed it to starve until its weight was reduced to 

 16 kgms. It was then fed for five days on a little meat and large 

 quantities of fat. At the end of that time it was killed and analyzed. 

 The body contained 1353 gms. of fat, of which only 131 gms. could 

 have come from the protein used, assuming that this material 

 can serve as a fat former. Much of the fat found, therefore, was 

 probably derived from the fat of the food. 



* Pfliiger, " Archiv f. die gesammte Physiologic," 51, 229, 1892, and 77, 

 521, 1899. 



t Lebedeff, " Centralblatt f. die med. Wiss.," 8, 1881, and Munk, "Vir- 

 chow's Archiv, " 95, 407, 1884. 



