CHLOROPHYLL AND ENERGY 187 



It caused great surprise to find this reaction in many 

 plants and even in animals — in the muscles, the hepatic tissue, 

 etc. Moreover, physiologists have given it an important place 

 in the chemistry of the cell, having observed, on the second 

 atom of carbon in most of the chemical substances found at 

 the great cross-roads of metabohsm, this ketone radical which 

 confers on their molecule a special reactivity. 



Pyruvic acid, oxalo-acetic acid and ketoglutaric acid all 

 have in their formula this group -CO-COOH, and that 

 alone v^ould be sufficient to indicate the importance of the 

 Wood and Werkmann reaction. It must therefore be concluded 

 that the fixation of carbon dioxide by the living organism is 

 not peculiar to photosynthesis. 



This discovery, and the fact that luminous energy liberates, 

 in the first place, the oxygen from water and not the oxygen 

 from carbon dioxide, disturbed all the classic conceptions of 

 the chemistry of photosynthesis. 



It is curious to observe that all these theories attempted to 

 show how the construction of glucosides could be effected 

 from carbon dioxide, first reduced and then progressively 

 polymerized to glucose and starch, as though this synthesis 

 was made in isolation and without the intervention of sur- 

 rounding substances. The use of radioactive carbon proved 

 finally that the old theories must be abandoned. 



If the plant is provided with carbon dioxide, all the 

 molecules of which have their atom of carbon "labelled", 

 these atoms will be very quickly fixed by the plant and distri- 

 buted in a large number of compounds. 



Suppose the time of illumination is shortened to five 

 seconds, for example, and the plant is immediately plunged in 

 boiling alcohol so that the fixed carbon has no time to spread 

 to many secondary compounds. 



If the classic conceptions were correct, we ought to find 

 in the plant, carrier of C^^, many substances with a single 

 atom of carbon hke formaldehyde HCHO — which would not 

 have had time to polymerize — some dicarbonate substances 

 like oxalic acid COOH-COOH, and fewer tricarbonate 



