ORIGIN OF FATTY ACIDS 77 



the acids entering into the composition of the vegetable fats 

 invariably contain an even number of carbon atoms. On these 

 grounds this theory of the formation of the fatty acids must 

 be rejected. 



Another question of importance in connection with the 

 fatty acids is whether the acids of lower molecular weight have 

 been derived from those of higher molecular weight ; or 

 whether, on the contrary, they represent stages in the building 

 up of acids of high molecular weight. The discovery by 

 Windaus and Knoop that in nature the point of attack upon 

 a fatty acid is the j3-carbon atom, has proved of considerable 

 importance. The process may be illustrated by a concrete 

 example : butyric acid is oxidised in the animal to £-hydroxy- 

 butyric acid 



CH 3 CH 2 CH 2 COOH + O -> CH 3 CHOH . CH 2 . COOH 



/?-hydroxybutyric acid 



a reaction which was first effected in vitro by Dakin with the 

 use of hydrogen peroxide. In general terms, an acid of the 

 formula R— CH 2 . CH 2 COOH is thus converted into an acid 

 R . CHOH . CH 2 COOH, and this, on further oxidation, yields an 

 acid RCOOH which, as will be seen, contains two atoms of 

 carbon less than the original acid. This method of oxidation 

 thus accounts for the production by metabolic oxidation only 

 of acids with an even number of carbon atoms, assuming the 

 original acids to have contained an even number. 



The alternative suggestion that acids of high molecular 

 weight are built up from those of lower molecular weight is 

 one which is more acceptable in explaining the production of 

 fatty acids from carbohydrates. 



It was first suggested by Nencki * that in the production 

 of butyric acid from lactic acid by fermentation, acetic alde- 

 hyde was an intermediate stage ; the changes involving the 

 formation of a four-carbon fatty acid (butyric acid) from a 

 three-carbon acid (lactic acid) could be accounted for as 



follows : — 



CH 3 CHOHCOOH = CH 3 CHO + CO a + H 2 . 

 Lactic acid Acetic aldehyde 



♦Nencki: "J. prakt. Chem.," 1878, 17, 105. 



