130 METABOLISM AND NUTRITION 



the larvae. Moreover, as O. Franck has shown, the method of determining the 

 fat, which was employed by Hofmann, does not permit of any positive conclu- 

 sion from his experiment. 



When we examine these observations critically, we must conclude with 

 Pfliiger that no single experiment has yet been given which proves beyond 

 question that fat is formed from proteid. Since, however, most of the proteids 

 contain a carbohydrate group and the body in all probability can form glyco- 

 gen at the expense of proteid, and since carbohydrates are unquestionably a 

 source of fat, the possibility of a final production of fat from proteid cannot 

 be excluded entirely ; although to judge from results thus far obtained, such a 

 roundabout production is not large and never takes place except with a very 

 rich supply of proteid. In man a transformation of proteid into fat is scarcely 

 to be admitted at all, for he has the power to digest and absorb only a rela- 

 tively small quantity of proteid. 



On the other hand, we have any number of experiments which show that 

 fat can be formed in the body from nonnitrogenous substances. 



That fat given in the food can be directly stored in the body, follows from 

 the experiments of Pettenkoffer and Voit cited on page 104, and is shown 

 with particular clearness by the following experiment of I. Munk. 



Munk let a dog starve for thirty-three days, during which time most of the 

 fat was of course lost from his body. He then gave the dog 300 g. meat and 

 160 g. rape-seed oil daily for seventeen days, and killed him at the end of that 

 time. On dissection a very large deposit of fat was found, which could not pos- 

 sibly have been derived from the meat fed. This in itself showed that the fat 

 of the oil had been stored; but in addition to this erucic acid, which is a con- 

 stituent of rape-seed oil but does not occur in dog fat, could be demonstrated in 

 the fat laid down from the food. 



Moreover, soaps and free fatty acids of the food can, after synthesis into 

 neutral fat, be directly stored in the body. This Radziejewski and Munk have 

 shown in the same way as in the experiment just mentioned, by feeding a soap 

 of rape-seed oil and the fatty acids set free from mutton fat, respectively. 



Whether or not fat can be formed from carbohydrates in the body, is a 

 question which has been discussed for a long time. Since the latter spare fat 

 from being metabolized, great importance has always attached to them in 

 the laying on of fat, and weighty reasons were found for such a transformation 

 in the case of herbivorous animals and especially of swine and cattle, which 

 are fattened for the market very largely on carbohydrates. Thereupon, the 

 discussion turned to carnivorous animals and man; and it has now been 

 completely demonstrated by I. Munk and Rubner in experiments which we 

 cannot go into here, that the transformation takes place in these also. 



We see, therefore, that fattening always occurs if the supply of nonnitroge- 

 nous substances is greater than the needs of the body. Under such circum- 

 stances the body can store almost any quantity of fat. Underneath the skin, 

 around the internal organs, in short everywhere in the body, fat can be accu- 

 mulated. 



