24 INTR OD UCTION. 



Bouilhac and TrSbaux, by painting a thin layer of gelatine with 

 a benzene solution of chlorophyl, secured a mechanism which on 

 exposure to sunlight actually decomposed carbonic acid into formic 

 aldehyde and hydrogen peroxide. We thus have a probable expla- 

 nation of the manner in which the carbohydrates may be constructed, 

 as they are essentially polymeric compounds of formic aldehyde 

 (6 X CH 2 O = C 6 H 12 O 6 ). Bouilhac and TrSbaux further showed 

 that Elodea forms starch in the dark from an 0.001 per cent, solu- 

 tion of formic aldehyde. The initial step in the assimilation of car- 

 bon is thus manifestly independent of living protoplasm. But since 

 chloroform vapor prevents the polymerization of formaldehyde it 

 would seem that the latter process cannot be caused by an enzyme. 



The same writers also found that on painting the white petals of 

 Saxafraga Wallacei, which can form starch from very dilute solu- 

 tions of formic aldehyde, with their benzene-chlorophyl solution, 

 the petals became capable of forming starch from carbon dioxide 

 and water, directly, in the sunlight. Formic acid is formed as an 

 intermediary product and from it Elodea has been shown to con- 

 struct starch in the sunlight. 



The hydrogen peroxide which is formed, together with formic 

 aldehyde, as indicated above, is decomposed into water and oxygen 

 by catalase, which is found in the chloroplasts of chlorophyl-bear- 

 ing plants. 



Glucosides. Closely related to the carbohydrates proper, the 

 origin of which has just been considered, is a group of substances 

 which likewise occur widely distributed in the vegetable kingdom. 

 These are the so-called glucosides. They are so termed from the 

 fact that glucose is invariably formed during their hydrolytic 

 decomposition, which, as an anhydride, thus constitutes an integral 

 part of their molecule. This observation at once suggests their 

 origin also from formic aldehyde. 



Such substances are salicin, which on hydrolytic decomposition 

 yields glucose and saligenin ; arbutin, which yields glucose and 

 hydroquinon ; phloridzin, which gives rise to glucose and phlore- 

 tin, etc. 



(1) C 13 H 18 7 + H 2 = C 7 H 8 2 + C 6 H )2 6 . 



Salicin. Saligenin. Glucose. 



(2) C 12 H 16 7 + H 2 == C 6 H 6 2 + C 6 H 12 6 . 



Arbutin. Hydroquinon. Glucose. 



(3) C 21 H 24 10 + H 2 = C 15 H U 5 + C 6 H 12 6 . 

 Phloridzin. Phloretin. Glucose. 



Especially interesting is a group of glucosides which are nitro- 

 genous in character, and thus stand, as it were, midway between the 

 carbohydrates and the albumins. A study of their decomposition- 

 products hence permits an insight into the manner in which the 

 albumins are synthetically produced, and shows that here also alde- 

 hyde groups play an important part. As in the case of the albu- 

 mins, the nitrogen here also occurs in combination with carbon and 



