798 NUTRITION AND HEAT REGULATION. 



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

 being useful only to protect a part of this proteid 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- 

 teid 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. f 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 proteid 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. 



Origin of Body Fat from Carbohydrates. That the body 

 fat may have this origin has been made probable or certain by 

 feeding experiments. Thus, Rubner fed a dog (5.89 kgms.) for 

 two days on a diet of sugar, starch, and fat whose total carbon 

 content was equal to 176.6 gms. During this period the animal 

 excreted 87.1 gms. of carbon. There were retained in the body, 

 therefore, 89.5 gms. carbon. The fat fed, 4.7 gms., contained 

 (4.7 X 0.77) 3.6 gms. C. The total nitrogen excreted during this 



* Pfluger, " 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. 



