HISTORY OF DIFFERENT FOODSTUFFS IN BODY 1045 



own particular kind of chyle fat. Very similar modifications must also 

 be effected by the tissue cells themselves, because the fats are in all 

 probability rehydrolyzed here, to become at least in part important 

 constituents of the protoplasm. This deduction is in no way refuted 

 by the fact that starving animals, when fed on foreign fat, are capable 

 of storing this substance practically unaltered. This merely proves 

 that it can be utilized in this form. Thus, Munk 1 has shown that an 

 animal fed on colza oil, deposits fat from which erucic acid may be 

 obtained, this acid being the basis of the glyceride contained in that 

 oil. In a similar way, it has been demonstrated by Lebedeff 2 that the 

 feeding of linseed oil or mutton fat to different dogs gives rise to a 

 deposition of body fat which is characterized by a different melt- 

 ing point; that derived from mutton suet remaining solid at 50 C. 

 Furthermore, Liebig has pointed out that the fats of different animals 

 present certain peculiarities in their appearance, consistency, melting 

 point, and general chemical properties, and are in turn different from 

 the fat ordinarily ingested with the food. In fact, many animals, such 

 as the herbivora, do not eat fat, although they often acquire a consid- 

 erable amount of body fat. But this is really an old established fact, 

 and has been used scientifically by Larves and G. Wert in their feeding 

 experiments upon pigs. 



These data have led in the course of time to various theories re- 

 garding the origin of the body fat. The modern view, which has been 

 placed upon a solid experimental basis by Pfltiger, 3 holds that it origi- 

 nates in part from the fat and in part from the carbohydrate of the food. 

 But the possibility that fat may also be derived from proteins, cannot 

 be excluded, because since the latter are deaminized and converted into 

 sugar and glycogen, these products may in turn be transformed into 

 fat. The proteins, however, cannot form an important source of fat 

 under ordinary conditions, because they constitute a relatively small 

 portion of the daily ingesta. 



While it cannot be stated definitely which of the first two sources 

 is the more important, the fat of the food is no doubt the chief element 

 in the carnivora, and the carbohydrate in the herbivora. Man, in all 

 probability, makes considerable use of the carbohydrates, because they 

 are really more easily reduced than the fats. Beyond this mere fact, 

 little is known regarding the manner in which this conversion is ac- 

 complished. It involves, of course, a change of oxygen-rich sugar 

 into oxygen-poor fat. Thus, if this process may be illustrated with 

 stearic acid, it will be found that three molecules of glucose (C 6 Hi 2 O 6 ) 

 give stearic acid (Ci 8 H 36 2 ) under an evolution of 16 atoms of oxygen 

 The fact that such a transformation gives rise to a liberation of oxygen 

 is shown by animals who are depositing fat on carbohydrate food. 



C*O 

 Their respiratory quotient, -^r-^' is increased considerably, because 



U2 



1 Virchow's Archiv, xcv, 1884, 407. 



2 Centralbl. fiir die med. Wissensch., 1881. 



3 Pfluger's Archiv, Ixxvii, 1899, 521. 



