890 PHYSIOLOGY 



accounting for its formation from the carbohydrates. By a simple 

 splitting of glucose, we may obtain two molecules of glyceraldehyde, 



CH 2 OH 



CHOH 



| OH 2 OH 



CHOH 



= 2 CHOH 

 CHOH | 



| CHO 



CHOH 



CHO 



which by reduction is readily converted into the corresponding 

 alcohol glycerine, CH 2 OH . CHOH . CH 2 OH. 



We may conclude then that fats are formed by the body with 

 ease from carbohydrates, and that in all probability this change 

 involves a building up of the fatty acid from the lower members 

 of the successive addition of a group containing two atoms of carbon. 

 The whole change, as Leathes has shown (v. p. 134), is an exothermic 

 one. For the formation of one molecule of palmitic acid, four mole- 

 cules of glucose would be required, and 12-5 per cent, of the total 

 energy of the glucose would be set free as heat. 



THE FORMATION OF FAT FROM PROTEINS. Among the 

 decomposition products of proteins the amino- derivatives of the 

 fatty acids take a prominent part. It would seem therefore highly 

 probable that by a process of deamination these amino-acids should 

 be first converted into fatty acids, which in their turn would be built 

 up by the process we have just discussed into the higher members 

 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 Pfluger 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. Pfluger showed that these conclusions were 



