CARBOHYDRATES AND FATS. 829 



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 

 period was 2.55 gms., which indicated a metabolism, therefore, of 

 16 gms. (2.55 X 6.25) of body protein. Making the improbable 

 assumption that all of the carbon of this protein was retained in 

 the body, this would account for 8.32 gms. C (16 X 0.52); so that 

 3.6 -r 8.32 or 12 gms. C might have originated from sources other 

 than the carbohydrate of the food, leaving, therefore, 89.5 12 

 or 77.5 gms. of C, which could have arisen only from the carbohy- 

 drate. This quantity of carbon could have been retained only as 

 glycogen or fat. Allowing for the greatest possible storage of 

 glycogen, 78 gms. or 34.6 gms. C, there would still remain 42.9 gms. 

 of C, which could have been retained only as fat. Numerous other 

 fattening experiments of different kinds have been made in which 

 it has been shown that the fat laid on by the animal could not be 

 accounted for by the fat of the food, nor by assuming with Voit that 

 it originated from the protein. The combined testimony of these 

 experiments have satisfied physiologists that the tissues can pro- 

 duce fat from sugar. The chemistry of the change is not understood 

 and cannot be imitated in the laboratory. 



The Source of Body Fat in Ordinary Diets. For the pur- 

 poses of demonstration the experiments made to prove the origin 

 of body fat from carbohydrate or the fat of food have made use 

 of abnormal diets and conditions. It would be a matter of practical 

 interest to ascertain whether upon normal diets the fat of the 

 body arises more easily from the fat or from the carbohydrate of 

 the food. While the question is one to which a positive answer 

 cannot be given, it seems to be probable that the result varies with 

 conditions and the nature of the animal. Experience seems to 

 show that carnivorous animals can be fattened more easily on a 

 fat diet, herbivora on a carbohydrate diet. In animals, like our- 

 selves, there is reason to believe that the carbohydrates are more 

 easily and more quickly destroyed in the body than the fats, and 

 that, therefore, the latter may be more readily deposited in the tis- 

 sues, although an excess of carbohydrate beyond the actual needs 

 of the body will also be preserved in the form of fat or glycogen.* 



The Cause of the Deposit of Body Fat Obesity. Our 

 experience shows that individuals differ greatly in the ease with 



* Consult Rosenfeld, 'Ergebnisse der Physiologic, " vol. i, part i, 1902. 

 Complete literature. 



