118 



PHYSIOLOGY 



CH S 



CH 3 



2| I 



CHO CHOH 



I 

 CH 2 



I 



CHO 

 aldehyde aldol 



Aldol reacts with water and undergoes a shifting of its OH and H groups, 

 in a manner with which we are already familiar as occurring in the conversion 

 of glucose into lactic acid, forming butyric acid. We may represent the 

 reaction in the following way, placing the water molecules opposite those 

 groups of the aldol molecule with which they react : 



CH 3 



I 



H HO CH H 



CH 2 



I 

 OH O C H 



OH 



gives 



2H 2 O 



CH 3 



I 

 CH 2 



I 

 CH 2 



I 

 COOH 



It will be seen that although water must enter into the reaction there is 

 no addition of water to the aldol in order to form the butyric acid. 



It has been suggested that similar reactions might account for the forma- 

 tion of the higher fatty acids, in which case one molecule of acetic aldehyde 

 would be added to the fatty acid in order to build up the acid which is next 

 highest in the series. Although certain of the higher acids have been pre- 

 pared in this way, proof is still wanting that a continuous series of SVM-- 

 theses may be effected by the continuous addition of aldehyde. Such a 

 hypothesis is however more probable than the direct conversion of three 

 molecules of sugar into one molecule of stearic acid. The latter change 

 would be associated with a very great absorption of energy, whereas a con- 

 tinuous building up of fatty acids, by the addition of aldehyde obtained 

 through lactic acid from the disintegration of hexose molecules, requires only 

 a small expenditure of energy, which could be obtained by the combustion 

 of the formic acid formed as a by-product in the process. If we suppose that 

 the synthesis of the higher fatty acids from sugar is carried out in this way. 

 the energy equations would he as follows (Leathes ) : 



1 g. mol. glucose 

 677-2 cals. 



H 



2 g. mnls. aldehyde + 2 g. mols. formic acid. 

 2 + 275-5 +2 X 151-7 

 = 6744 cals. 



