THE MECHANISM OF ORGANIC SYNTHESIS 125 



(6) The leaves were distilled in a current of steam. The distillate was 

 shown to contain formaldehyde by the formation of methylene aniline crystals 

 on treatment with aniline, and by the preparation from it of the characteristic 

 tetrabrome derivative of hexamethylenetetramine. 



Usher and Priestley conclude that the first products of the photo- 

 lysis of carbonic acid are hydrogen peroxide and formaldehyde. Both 

 these substances are rapidly removed from the reaction. The hydrogen 

 peroxide is broken up by the catalase into water and oxygen which 

 is turned out by the plant. The formaldehyde is at once polymerised 

 in the protoplasm of the chloroplast with the formation first of a 

 hexose and then of starch. The formaldehyde, if not removed in this 

 way, destroys the catalase. The hydrogen peroxide, if not broken 

 up by the catalase, destroys the chlorophyll. 



The relations between the various factors in this process may be 

 diagrammatically expressed thus : 



Carbon dioxide + Water 



i f 



(// not removed, destroys) > CHLOROPHYLL 



Hydrogen peroxide + Formaldehyde 



.-(// not removed, poisons) 

 ENZYME LIVING PROTOPLASM 



>1^ ^X' 



Oxygen Carbohydrates 



In thus reducing certain of the stages in the assimilation of carbon 

 to phenomena which can be imitated outside the living organism we 

 have made considerable strides in the ' understanding ' of the pro- 

 cess. The stage for which the vitality of the chloroplast is absolutely 

 essential is the formation of starch from formaldehyde. Outside the 

 body, our polymerisation of formaldehyde results in the formation of 

 a mixture of sugars which are optically inactive. The same process, 

 in the living cell, leads to the production of optically active sugars 

 which are connected stereochemically and mutually convertible one 

 into the other, e.g. fructose and glucose. The derivatives of protoplasm, 

 containing asymmetric carbon atoms, are in the same way optically 

 active, and it seems that the asymmetry of the protoplasmic molecule 

 conditions a corresponding asymmetry in the substance which it 

 builds on to itself. The protoplasm furnishes, so to speak, a mould 

 in which polymerisation of formaldehyde can result only in the produc- 

 tion of sugars of certain definite stereochemical configurations. 



Few, if any, chemical reactions are pure. Nearly all are attended 

 with by-reactions, so that the yield of end product never attains 



