PHYSIOLOGICAL FORMATION OF FAT 333 



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 animal until it is as free from fat as possible, then 

 feeding with a large amount of some fat that is of a type dif- 

 ferent from that normally found in the animal ; the new fat 

 that is then laid up in the fat depots 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 resemble the fat of 

 the food. 1 As a matter of fact, the body 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, 

 varying somewhat in composition in the different fat depots in 

 the same body, and apparently being more or less modified by 

 diet. 



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

 to Rosenfeld, this fat differs from the fat formed on mixed diet 

 in having less olein in proportion to the palmitin and stearin, 

 and it is deposited particularly in the subcutaneous and mesen- 

 teric tissues rather than in the liver. Man does not seem to 

 form fat readily from carbohydrates, but rather burns them to 

 protect his proteids ; on the other hand, swine and geese readily 

 form fat from carbohydrates. As the fatty acid radicals of 

 ordinary fat (C^H^O^ C 16 H 32 O 2 , C 18 H 34 O 2 ) are much larger than 

 the carbohydrate radicals, a process of synthesis must be in- 

 volved in the formation of fat from carbohydrates. 2 



(3) Proteids are a possible source of fat, but it has not been 

 established 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 state- 

 ment rests our present tendency to refute the long-cherished 

 conception of fatty degeneration as a true degeneration of cell 

 proteids into fat, as suggested by Virchow. This view was 

 supported by the earlier work of Voit and his school, who be- 

 lieved that they had demonstrated that animals could form fat 

 from proteid food, and their work was for a long time accepted 

 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 



1 See Engel, Zeit. physiol. Chera., 1905 (44), 353. Thiemich (Jahrb. f. 

 Kinderheilk., 1905 (61), 174) has also found evidence that the fat of the fetus 

 is transported from the fat depots of the mother. 



2 This, Magnus-Levy suggests, may he accomplished through lactic acid 

 which is formed from sugar, and then, after reduction to an aldehyde, several 

 of these molecules are combined into the higher fatty acid. See Leathes, loc. 

 cit., p. 82. 



