THE METABOLISM OF FAT 555 



supposed to furnish an absolute proof of the formation of fat from 

 protein, under strictly physiological conditions, although in a humble 

 form of animal life. Maggots were allowed to develop from the egg on 

 blood containing a known amount of fat. The quantity of fat in the 

 eggs was also known. After the maggots had grown, ten times as 

 much fat was found in them as had been contained in the blood and 

 eggs together. The trifling quantity of sugar in the blood was utterly 

 inadequate to account for the fat, which, it was concluded, must there- 

 fore have come from the proteins of the blood (Hofmann). It can be 

 objected to this experiment that no precautions were taken to prevent 

 the growth of micro-organisms on the blood, and fat might have been 

 formed by them from the proteins. Further, the fat estimations would 

 scarcely pass muster according to the present standards. 



The experiments of Pettenkofer and Voit, which were supposed to 

 have demonstrated that in the higher animals also fat is formed from 

 proteins under normal conditions, are in the same position. According 

 to them, a dog fed for a time on a liberal diet of lean meat may go on 

 excreting a quantity of nitrogen equal to that in the food, while there 

 is a deficiency in the carbon given off. Or if the dog is not in nitrog- 

 enous equilibrium (p. 591), but putting on nitrogen in the form of 

 ' flesh/ the deficiency in the carbon given off may be too great in pro- 

 portion to the nitrogen deficit to warrant the assumption that all the 

 retained carbon has been put on in the form of protein. In either case, 

 carbon in large amount can only come from the proteins of the food, 

 and can only be stored up in the body in the form of fat. For lean meat 

 contains but a trifling quantity of carbon in any other proximate 

 principle than protein, and the non-protein carbon of the animal body 

 is only to a very small extent contained in carbo-hydrates or other 

 substances than fat. 



Pfliiger has criticized these experiments, and has shown that lean 

 meat contains more fat than was supposed, and this is now generally 

 admitted. He has endeavoured to show that the fat and 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 indications 

 of its possibility and of its actual occurrence. The accumulation 

 of fat between the hepatic cells caused by phlorhizin is, at the best, 

 no better evidence than the accumulation within the cells in phos- 

 phorus 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 



