SOURCE OF THE BODY FAT 



465 



observation is strongly supported by the work of Eckles on the variation in 

 the percentage of fat in the milk of dairy cows under the influence of tempo- 

 rary short feed. If a cow is given an insufficient amount of food immediately 

 the percentage of fat in the milk sharply increases, sometimes amounting to 

 almost double the original fat content of the milk. 



Source of the Body Fat. Excess of fat in the food can be stored as 

 fat in the body. This fact is demonstrated by Voit, Hoffmann, Rubner, 

 and others. Rubner states that 82 to 92 per cent, of the fat excess can be 

 stored. The fat stored was long thought to be the same kind given in the 

 food, even though the usual fat of the animal was different. The melting 

 point of dog's fat is about 20 C, but by feeding an excess of mutton fat the 

 melting point has been raised to 40 C. The subcutaneous fat of pigs sub- 

 jected to this experiment is more or less fluid according to the melting point 

 of the fat fed. However, we now know that this conception is only partially 

 correct. The physical and chemical constants show that the fat laid down 

 approaches in characteristics the fat fed, but that it is not the same. Even 

 in the alimentary canal during digestion, changes occur which modify the 

 melting point and other properties of remnants of the fat not absorbed. Fat 

 that is resynthesized in the mucous epithelium after absorption is similar 

 but not identical with the fats of the food. This possibly rests upon a varia- 

 tion in the number and character of the unsaturated bonds during fat 

 mobilization in the body. 



The body fat can also be derived from carbohydrate food, a fact which 

 the practices of the stock feeder and dairyman constantly verify. The ex- 

 periments will present the matter more vividly than pages of description. 



GAIN IN FAT OF A PIG FED ON RICE. (MEISSL AND STROHMER.) 



It is obvious that the 5.3 grams of fat and the 66 grams of protein cannot 

 account for the carbon retained, and one must look to the carbohydrate as 

 the source of the fat. 



Jordan placed a Jersey cow on a feed of hay and grain from which the 

 fat was extracted. The cow in 95 days assimilated 5 . 7 pounds of fat, in- 

 creased 47 pounds in weight, and produced 62.9 pounds of fat in the milk. 

 The nitrogen excreted was the equivalent of 33.3 pounds of protein. The 

 non-nitrogenous moiety of the protein, if its carbon had all gone into fat, 



