THE MECHANISM OF ORGANIC SYNTHESIS 119 



2 g. mols. aldehyde j J 1 g. mol. aldol j fl g. mol. butyric acid. 



551 cals. ( 546-8 cals. j -\ 517-8 cals. 



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



4 g. mols. glucose | f 1 g. mol. palmitic acid + 8 g. mols. formic acid. 



2708 cals. J j 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 avail- 

 able 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. 



Attempts to produce the higher fatty acids by the condensation of successive 

 molecules of aldehyde have so far resulted only in the production of branched chains 

 of carbon atoms, whereas the normal fatty acids of the body are straight chains ; 

 though Raper has shown that the normal caproic acid may be formed by the condensa- 

 tion of aldol with itself. Miss Smedley has suggested that a more probable line of 

 synthesis lies through pyruvic acid. Pyruvic acid, which may be produced in the body 

 from lactic acid, and so from carbohydrate, is fermented by yeast with the production of 

 acetaldehyde and carbon dioxide, by means of a ferment carboxylase. If we assume 

 the existence of a similar ferment in the cells of the body, it would split this acid into 

 aldehyde and CO 2 . Aldehyde however combines with a molecule of pyruvic acid to 

 form a higher keto =acid, which might either be oxidised to the fatty acid containing one 

 carjbon atom less, or might be again transformed by enzymes into an aldehyde capable 

 of reacting with another molecule of pyruvic acid. These changes are represented in the 

 following equations: 



CH 3 CO.COOH = CH 3 CHO + CO 2 

 CH 3 CHO + CH 3 CO.COOH = CH 3 CHOH.CH 2 .CO.COOH 

 CH 3 CHOH.CH 2 .CO.COOH + O == CH 3 CHOH.CH 2 COOH + C0 2 



/3-oxyacids would thus be a normal stage in the building up as well as in the breaking 

 down of fatty acids. 



The glycerin which enters into the formation of the ordinary neutral 

 fats can be synthetised by both plants and animals, and there is every 

 ground for believing that it, like the fatty acids, may be derived from 

 carbohydrates. We have already seen that in the conversion of glucose 

 into lactic acid the first step is the formation of glyceric aldehyde, 



