CARBOHYDRATES AND FATS. 799 



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

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

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

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

 3.6 + 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 or by assuming with Voit that it 

 originated from the proteid. The combined testimony of these 

 experiments have satisfied physiologists that the fat tissues can 

 produce fat from sugar. The chemistry of the change is not under- 

 stood and can not 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 originates most easily from the fat or from the carbohydrate 

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

 can not 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 may 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 

 which they form fat. Some upon relatively small diets form much 

 fat, while others remain thin in spite of the ingestion of large 

 amounts of food. Voit has indicated the general reason for this 

 difference, namely, that it depends upon the capacity of the body 

 to destroy food material. When food is supplied and absorbed 

 in excess of this capacity the excess is stored mainly as fat, 

 and to a small extent as glycogen or as new proteid. A diet, there- 

 fore, which will give such an excess to one individual may in the 



* Consult Rosenfeld, " Ergebnisse der Physiologie, " vol. i, parti, 1902. 

 Complete literature. 



