436 PROCESSES INFERRED FROM INDIRECT OBSERVATION 



We must expect to find formaldehyde in vegetable tissues, if it 

 occurs therein at all, therefore, only in minute traces. Now although 

 we possess very sensitive reagents for aldehydes, yet these do not as a 

 general rule exclude the possibility of much more complex aldehydes 

 than formaldehyde being present and yielding the reaction. Even 

 Proteins and many other tissue-constituents will yield reactions indica- 

 tive of an aldehyde-grouping. This would not perhaps constitute an 

 insurmountable difficulty if it were not for the fact, as we have seen, 

 that the aldehyde we are seeking to identify is at the most only present 

 in minute traces. 



Another way of attacking the problem might appear to be feasible, 

 namely that of extracting Chlorophyll from green plants and utilizing 

 its light-activating properties to bring about the synthesis of for- 

 maldehyde in laboratory-glassware, apart from the complications and 

 secondary reactions which attend the process in living tissues. Numer- 

 ous attempts to accomplish this have failed. According to Usher and 

 Priestley, however, the source of failure has resided in the employment 

 of comparatively thick layers of the chlorophyll solution. If we blow 

 carbon dioxide through a test-tube or flask filled with chlorophyll and 

 exposed to light, we cannot expect to observe much photosynthesis, 

 because the most superficial layers of the chlorophyll solution will 

 absorb all of the active light-rays and transmit to the underlying 

 solution only those which are chemically inactive. In the living plant 

 the chlorophyll is disposed quite differently. Here we observe that 

 pigment is confined to exceedingly thin layers at the surfaces of a series 

 of bodies known as the Chloroplasts in which active photosynthesis 

 can be shown to be proceeding during illumination. Usher and 

 Priestley have sought to imitate this architecture of the photosynthetic 

 apparatus, by painting the surfaces of plates of gelatin with a thin 

 layer of chlorophyll and then blowing carbon dioxide over them and 

 exposing them to light. Under these conditions they state that a 

 comparatively rapid disengagement of oxygen occurs, the surface film 

 becoming wrinkled and distorted by the accumulation of bubbles of 

 oxygen below it, while very evident quantities of formaldehyde are 

 found in the underlying gelatin. The accumulation of formaldehyde 

 in this case, as contrasted with its evanescence in the tissues of plants 

 they refer to the absence of the enzymes necessary to accomplish the 

 removal of the formaldehyde by condensation, which, in the plants, are 

 present in the underlying substance of the chloroplasts. Against this 

 experiment it has been urged by several investigators that the presence 

 of formaldehyde in gelatin jellies is very difficult to establish, since 

 most samples of gelatin themselves yield a very pronounced aldehyde- 

 reaction. Usher and Priestley, however, state that the gelatin which 

 they employed was free from aldehydes. On the other hand the syn- 

 thesis of formaldehyde and other products from carbon dioxide and 

 water has frequently been accomplished without the intermediation of 

 chlorophyll by the use of the silent electric discharge, and by exposure 



