134 PHYSIOLOGY 



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 

 formation 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 prepared in this way, proof is still wanting that 

 a continuous series of syntheses 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 continuous building up of fatty 

 acids by the addition of aldehyde obtained through lactic acid from the 

 disintegration of hexose molecules only requires 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 syn- 

 thesis of the higher fatty acids from sugar is carried out in this way, 

 the energy equations would be as follows (Leathes) : 



1 g. mol. glucose ) (2 g. mols. aldehyde + 2 g. mols. formic acid. 



677-2 cals. ft 2 x 275-5 + 2 x 61-7 



- 674-4 cals. 



2 g. mols. aldehyde ) fig. mol. aldol V__ : fig- mol. butyric acid. 



551 cale. J " > t 546-8 cals. / ~ ^\ ~ 517-8 cals. 



Or, tracing the same change on as far as palmitic acid : 



4 g. mols. glucose ) / 1 g. mol. palmitic acid + 8 g. mols. formic acid. 



2708 cals. / \ 2362 cals. + 494 cals. 



-= 2856 cals. 



In the first stage of the synthesis, the reaction leading to butyric acid, 

 the net result would be, supposing the formic acid to be oxidised, that 

 some 160 calories, or nearly 25 per cent, of the whole energy, would be 

 rendered available for other purposes. In the latter stages leading 

 to palmitic acid some of the energy derived from the oxidation of the 

 formic acid would be required for effecting the synthesis, and only about 

 12-5 per cent, of the original amount contained in the sugar would be 

 set free. It is worth noting that in the butyric fermentation of sugar 

 by micro-organisms there is a production first of lactic acid, and this 

 substance then disappears to give place to butyric acid. At the same 

 time carbonic acid and hydrogen are evolved, both gases being derived 

 from the decomposition of the formic acid. In the process a certain 

 amount of caproic acid is always produced, and the crude butyric acid 

 of fermentation is used as the source from which commercial caproic 

 acid is derived. 



The glycerin which enters into the formation of the ordinary 



