266 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



as was explained in Chapter IV, is formaldehyde, CH 2 0. Von 

 Baeyer suggested that, in the simultaneous presence of light 

 and of chlorophyll, carbon dioxide and water may react 

 according to the following simple equation : 



C0 + H0 = CH0 + : 



An explanation is here indicated of the equivalence alluded 

 to above between the C0 2 decomposed and the oxygen evolved. 

 It is easy to conceive further, that the formaldehyde, by a 

 series of polymerisations, can build up more complex carbo- 

 hydrates, such as starch. This hypothesis derives confirma- 

 tion from the fact that, on standing in contact with a dilute 

 solution of lime water, formaldehyde does, as a matter of fact, 

 become gradually converted into a mixture of hexoses. Until 

 recently, however, all attempts to realise the formation of 

 formaldehyde from carbon dioxide and water in the laboratory 

 were without success, formic acid being always the product 

 of the reaction. Nor was it possible to detect formaldehyde in 

 the living cell. 



Recently, however, the subject has been advanced con- 

 siderably by the investigations of Usher and Priestly ; they 

 have been able to show that if leaves of Canadian pond weed, 

 Elodea canadensis, and certain green seaweeds, viz., Ulva and 

 Enter omorpha, are first placed in hot water, so as to kill the 

 protoplasm, and are then exposed to moist carbon dioxide 

 in presence of light, formaldehyde and hydrogen peroxide are 

 produced, and can be detected. If a suitable catalase, or 

 hydrogen peroxide decomposing enzyme, were introduced into 

 the mixture, oxygen was evolved. 



Under the conditions of the experiment, when a certain 

 amount of hydrogen peroxide and formaldehyde had been 

 formed, a reverse change tended to be set up, the reaction 

 being expressed as follows : 



H 2 C0 8 + 2H 2 CH 2 + 2H 2 2 



