398 RETROGRESSIVE CHANGES 



(1) A large proportion of the fat of the body comes from the 

 fat taken in the food, as also does the fat of the milk. This can be 

 shown, as Rosenfeld particularly demonstrated, by starving- an ani- 

 mal until it is as free from fat as possible, then feeding with a large 

 amount of some fat that is of a type different from that normally 

 found in the animal ; the new fat that is then laid up in the fat de- 

 pots of the animal will partake of the characters of the fat given in 

 the food. In case the animal is lactating, the milk-fat will also resem- 

 ble the fat of the food. As a matter of fact, the bod}- fat is not of 

 constant composition, even in the same individual ; it varies greatly 

 with age, having much less olein in infancy than in later years, vary- 

 ing somewhat in composition in the different fat depots in the same 

 body, and apj^areiitly being more or less modified hy diet. 



(2) Fat may also be formed from carbohydrates. According to 

 Rosenfeld, this fat differs from the fat formed on mixed diet in ha'v- 

 ing less olein in proportion to the palmitin and stearin, and it is de- 

 posited particularly in the subcutaneous and mesenteric tissues rather 

 than in the liver. ]\Ian does not seem to form fat readily from car- 

 bohydrates, but rather burns them to protect his proteins: on the 

 other hand, swine and geese readily form fat from carbohydrates. 

 As the fatty acid radicals of ordinary fat (CigH„|,,Oo, Cif.,H^2025 

 CigHg^Oo), are much larger than the carbohydrate radicals, a process 

 of synthesis must be involved in the formation of, fat from carbo- 

 hydrates. - 



(3) Proteins are a possible source of fat, but it has not been estab- 

 lished that they are either a common or an important source of fat in 

 either physiological or pathological conditions, or, indeed, that they 

 really ever do form fat. Upon this statement rests our present 

 tendency to refute the long-cherished conception of fatty degeneration 

 as a true degeneration of cell proteins into fat, as suggested by A^ir- 

 chow. This view was supported by the earlier work of Voit and his 

 school, who believed that they had demonstrated that animals could 

 form fat from protein food, and their work was for a long time ac- 

 cepted as correct. Later Pfliiger and his pupils pointed out what 

 seem to have been essential errors in these investigations, and, after 

 much discussion and experimentation, the majority of physiologists 

 now support the view advanced in the sentence opening this para- 

 graph. Since proteins contain carbohydrate groups, and since fats 

 can be formed from carbohydrates, the ]iossibility of the foi-mation of 

 fats from the proteins in this indirect way cannot be denied. It is 

 also possible that the nitrogen-containing groups may be split out of 

 the amino-acids of the protein molecule, and that the non-nitrogenous 

 residues can then be built up into fatty acid molecules as large as the 



2'1'liis. Ma^'inis Levy siifjposts, may 1k' iicc()iii|plislicil (lirduiih lactic acid wliicli 

 is forniod from siifjar. and tlicn, after reduction to an aldciiydo. several of tliese 

 molecules are eombined into the liijrlier fatty aeid. See Loathes, loc. cit., p. S2. 



