712 METABOLISM 



doubted diminution in acidosis which occurs in diabetes when carbo- 

 hydrate food is given is dependent upon the directive influence which its 

 combustion in the liver has on the above processes. But we must be 

 cautious not to transfer results obtained by experiments with minced 

 liver in judging of the reactions Avhich occur during life. Provisionally, 

 then, we must assume either that /Miydroxybutyric acid is a necessary 

 stage in the oxidation of butyric acid or that it is formed by reduction 

 of acetoacetic acid, which is really the first step in that process. 



Of course there is no evidence in the above experiments that the higher 

 fatty acids are also broken down by the removal of two C-atoms at a 

 time, nor has it been possible to detect any ketonic or /3-hydroxy deriv- 

 atives of them in the animal body. We can only reason from analogy 

 that a similar process may occur, although some support is furnished 

 for such a view by the fact that ketonic fatty acids have been found in 

 vegetable organisms. 



What, then, it may be asked, is the relation of the desaturation of fatty 

 acids which we have seen occurs in the liver (and probably elsewhere) to 

 the ft oxidation? There can be no doubt that both processes can occur 

 in the animal body, indeed in the same organ, e.g., the liver; and it is 

 important to ascertain their relationship to each other. The conclusion 

 Avhich would seem to conform best with the known facts is that the 

 desaturation process occurs (in the liver) so as to break up the long 

 fatty-acid chain into smaller chains, which are then capable of /? oxida- 

 tion (in the tissues) ; desaturation may be the process by which the mole- 

 cule is rough hewn, and /? oxidation that by which the resulting pieces 

 are finally split to their smallest pieces that is, to molecules of the size 

 of acetic acid, which are finally completely burnt to carbonic acid and 

 water. 



The increase of iodine value observed by Leathes and his coworkers need not, as has 

 already been pointed out, necessarily indicate that new double linkages have been intro- 

 duced in the fatty-acid chain ; it may merely indicate that structurally isomeric deriva- 

 tives which absorb iodine more readily have been formed. Direct evidence of desatura- 

 tion has, however, been offered by Hartley, who isolated the unsaturated fatty acids (by 

 dissolving the lead soaps in ether) from pig's liver and then proceeded to oxidize them 

 with alkaline permanganate. When the olein of the depot fat is thus treated at a low 

 temperature, two hydroxyl groups become attached where the double linkage existed 

 (forming dioxystearic acid), and when the mixture is now warmed, the molecule splits 

 into two at this place, forming two lower acids (pelargonic and azelaic) : 



(1) CH,-(CH,),CH:CH(CH 2 ).COOH; 

 (oleic acid) 



(2) CH,-(CH 2 ) I -CH 



OH OH 



CH (CH 2 ) 7 COOH; 



(dioxystearic acid) 



(3) CH, (CH S ) 7 COOH + COOH-(CH 2 ) 7 COOH. 



(pelargonic acid) (azelaic acid) 



