832 PHYSIOLOGY 



of the series. For many years, as a result of the investigations of Voit, 

 the proteins were indeed regarded as the chief, if not the sole, source of 

 the fats of the body, and it needed the energetic assaults of Pfliiger on this 

 doctrine in 1891, before it could be clearly examined by physiologists. 



Let us see what are the grounds for assuming a formation of fat from 

 protein. In the first place, there is a well-known experiment by Voit. 

 A dog was fed with large quantities of lean meat for a considerable time. 

 Voit found that the whole of the nitrogen of the intake was excreted, but 

 that a certain percentage of carbon was retained in the body, and that 

 the percentage of this carbon was greater than could be accounted for by 

 the deposition of glycogen in the liver and muscles. He therefore assumed 

 that it must have been laid down as fat. Pfliiger showed that these con- 

 clusions were not justified by Voit's results, and were really based on the 

 fact that too high a figure had been assumed for the carbon of the meat. 

 Whereas Voit found that the animal had laid on 56 grm. of fat during 

 one day of the experiment, a recalculation of the same results by Pfliiger 

 shows that the animal could not have put on more than 3-9 grm. of fat, 

 an amount which might quite well be accounted for by the fat and glycogen 

 present in the meat. Pfliiger has shown moreover that an animal may 

 be fed in any quantities for weeks on the leanest meat that it is possible 

 to procure, without putting on any fat at all; and, as we have seen, increasing 

 the ration of protein increases simply the nitrogenous and general 

 metabolism of the body. 



Although therefore we must assume that the healthy body does not 

 normally form fat from protein, there are certain pathological conditions 

 which seem at first to tell in favour of such a conversion. Thus during 

 certain diseases, such as diphtheria, pernicious anaemia, and as the result 

 of poisoning by phosphorus, the majority of the organs of the body undergo 

 acute fatty degeneration. The liver may be enlarged. All its cells are 

 studded with fat granules which are apparently formed by a change in 

 the protoplasm of the cells. This change was long interpreted as due to 

 a direct conversion of protein into fat. More exact analyses have shown 

 that during fatty degeneration the total fat in the body is not increased. 

 Thus one observer took 124 pairs of frogs and poisoned one of each pair 

 with phosphorus. The animals were then killed, and the whole of them 

 analysed. The difference in the content of fat between the poisoned and 

 unpoisoned animals fell within the limits of experimental error, so that 

 there had been no increase in the fat of the body as the result of the poison- 

 ing. In some of these cases the liver is actually enlarged, but this 

 deposition of fat in the cells is due to the immigration of the fat from other 

 parts of the body and not to conversion of the protein of the cells. This 

 is shown by the facts that the composition of the fat in the degenerated 

 liver varies according to the composition of the fat in the rest of the body, 

 and that, if abnormal fats are given with the food, such as erucic acid or 

 iodine fats, these are found in the fat extracted from the liver. In fatty 

 degeneration two processes are at work : one is the immigration of fats 



