116 PHYSIOLOGY 



When either of these arrangements reacts with water, thus : 

 CH 2 OH CH 2 OH 



CHOH CHOH 



OH.C.H OH COH-fH 2 



HOOH 



I 

 CHOH 



COH 



H 



CH 2 OH 



CHOH 

 COH 



we obtain two molecules of glyceric aldehyde, which then by a further 

 shifting of the OH and H groups becomes 



CH 3 



CH.OH 



COOH 



lactic acid 



Lactic acid with ammonia and some dehydrating agent will give amino- 

 propionic acid or alanine. The formation of the higher amino-acids in- 

 volves a process of reduction of the sugar first formed in the chlorophyll 

 granules. It is possible, however, that the starting-point for the amino-acid 

 synthesis may be, not a hexose itself, but some other substances, formed, 

 so to speak, as by-products in the assimilation of sugar from carbon dioxide. 

 We have seen reason to believe that the first result of the action of the sun's 

 rays within the chlorophyll corpuscle is formaldehyde. This substance in 

 the presence of calcium carbonate when exposed to the light gives a mixture 

 of glyceryl aldehyde and dihydroxy acetone. If we can assume that acetone 

 is formed from the latter by a process of reduction, we might possibly derive 

 leucine from an interaction of this substance with lactic acid and ammonia. 

 Thus: 



CH 3 CH 3 



CH, CH ? 



CO + CH.OH + NH, + H, 



CH 3 COOH 



\CH/ 

 CH 2 



CH.NH 2 

 COOH 



2H 2 



