I.— PHYSIOLOGY. 165 



of fat in animals have yielded very little so far. It was observed many 

 years ago by Leathes that the fat in the liver of some animals might 

 increase in amount if the organ were kept warm and mider sterile condi- 

 tions for a few days after its removal from the body. The addition of 

 glycogen or glucose does not however have any effect on this increase in 

 fat content. The process appears to be determined by something other 

 than a mere excess of carbohydrate, but what this is is not known. It is 

 however known that acetaldehyde and pyruvic acid, the intermediates 

 postulated in the hypothesis just mentioned, can be produced in the body. 

 Neuberg and Gottschalk detected acetaldehyde as a product of decarboxy- 

 lation of pyruvic acid in the liver and recently Hahn, Fischbach and 

 Haarmann have shown that under anaerobic conditions pyruvic acid may 

 be produced in muscle from lactic acid. But there the question rests for 

 the present so far as higher animals are concerned. When we know what 

 the conditions are which set the process of fat synthesis going, and when 

 we are able to reproduce them at will in animals, it may be possible to 

 determine what are the intermediate substances concerned. 



More success has been achieved by a study of the formation of fatty 

 acids in microorganisms, some of which possess this faculty in a remarkable 

 degree. Bacteria which form butyric acid from glucose have been found 

 to produce in addition both lactic acid and acetaldehyde. These same 

 bacteria will also produce butyric acid from pyruvic aldol though not from 

 aldehyde ammonia, aldol or pyruvic acid itself. Neuberg and Arinstein, 

 who investigated this type of fermentation, conclude that pyruvic aldol 

 is the precursor of the butyric acid when it is formed from carbohydrate. 

 This does not negative its production from acetaldehyde, since the addition 

 of sulphites to the fermenting liquid causes a fixation of acetaldehyde and 

 inhibits the production of butyric acid, thus suggesting that acetaldehyde 

 takes some part in the process. But it has also been shown that in this 

 so-called butyric fermentation fatty acids containing an even number of 

 oarbon atoms higher in the series than butyric are formed, namely, hexoic 

 and octoic acids. This makes it appear probable that the processes 

 by which these lower members of the series of fatty acids are formed 

 in bacterial fermentation may be the same as those by which higher 

 members of the series are formed in animals. The production of fat 

 is a process which is common to a great variety of living organisms 

 both simple and complex, animal and vegetable. It is not unlikely 

 therefore to be carried out by the same series of chemical reactions 

 wherever it is found. 



The intensive study during the last few years of the processes of alco- 

 holic fermentation and the chemical events which occur in muscular con- 

 traction has revealed such close similarities that we are becoming forced 

 to accept the view that certain fundamental activities of the living cell, 

 whether animal or vegetable, may be carried out by an almost identical 

 mechanism. It may therefore be that we shall eventually discover the 

 reactions responsible for the synthesis of fat in animals by investigating 

 the processes by which it occurs in vegetable forms, such as bacteria or 

 moulds. Before leaving the subject of fat synthesis it is worth while to 

 point out the economy of the suggested process of synthesis from lactic 

 acid by way of acetaldehyde. It is a good illustration of the kind of serial 



