METABOLISM, NUTRITION AND DIETETICS 527 



glycogen in the meat given to the animals fully accounts for the 

 carbon retained. Pfliiger, indeed, takes up the position that the 

 fat of the body comes exclusively from the carbo-hydrates and 

 fats of the food, and not at all from the proteins. But there is 

 little doubt that in this he has gone too far, although his criticism 

 has rendered it impossible any longer to appeal to Pettenkofer and 

 Voit's results as good evidence on the other side. 



If none of the supposed quantitative proofs of the conversion 

 of proteins into fat which have hitherto been brought forward are 

 free from flaw, the same is true of the alleged qualitative indica- 

 tions of its possibility and of its actual occurrence. The accumu- 

 lation of fat between the hepatic cells caused by phloridzin is, at 

 the best, no better evidence than the accumulation within the 

 cells in phosphorus poisoning. The formation of adipocere (a 

 cheesy substance, rich in fatty acids united with calcium or 

 ammonium), sometimes seen in dead bodies which have remained 

 a long time under water or in moist graveyards, is largely, if not 

 entirely, due to the fat already present in the parts which have 

 undergone the change, or to fat removed by the water from other 

 parts of the body. If any portion of the adipocere represents 

 fat formed from protein, this transformation may well be credited 

 to the numerous micro-organisms present, and throws no light 

 upon the question of fat formation in the normal organism. 

 The fat in the cells of the sebaceous glands, and of the mammary 

 glands, may be produced from protein by a transformation of the 

 cell-substance. But absolutely convincing proof is wanting. The 

 rule which experience has taught, that a woman during lactation 

 requires an excess of proteins in her food corresponding not only 

 to the proteins, but also to the fat given off in the milk, suggests 

 such an origin for the milk-fat, but does not prove it. 



As to the ultimate fate of the fat, from whatever source it 

 may be derived, our knowledge may be compressed into a single 

 sentence : Sooner or later it is split and oxidized to carbon dioxide 

 and water, its energy being converted into heat or, directly or in- 

 directly, into mechanical or chemical work ; some of the fat absorbed 

 from the intestine rapidly undergoes this change without entering 

 the fat-cells of the adipose tissue. A portion of the fat may be 

 changed into carbo-hydrates. This has been proved for the glycerin 

 component ; its possibility must be admitted for the fatty acids, but 

 complete proof has not yet been given. 



The mechanism of the, transformation of fats is no better under- 

 stood than that of the carbo-hydrates or the proteins. Many of 

 the tissues contain intracellular, soluble, fat-splitting ferments 

 called lipases, especially the liver, the active mammary gland, 

 and the intestinal mucosa. We have already seen that there 

 is evidence that these lipases, like some other enzymes, have a 

 reversible action. They are either fat-splitting or fat-forming 



