94 ACTION OF LIGHT KAYS 



formaldehyde were formed in abundance on exposure to light, this 

 would be of no avail as a proof of photo-synthesis of formaldehyde 

 from the inorganic, for the same change would happen in a solution 

 of cane sugar, and there is no proof that the chlorophyll is not 

 simply behaving like a legion of other organic compounds and yield- 

 ing formaldehyde by its own decomposition. 



It has recently been shown by Jorgensen and Kidd 1 that pure 

 chlorophylls, exposed as a suspension in water to light in presence 

 of oxygen, at first bleach and then yield formaldehyde. Under 

 natural conditions in the leaf and under all conditions of exposure 

 to light of artificial schemata, used by previous observers, there has 

 always been present atmospheric oxygen, so that this appearance of 

 formaldehyde from pure chlorophyll emulsions after exposure to 

 light confirms the view expressed above. 



In the second place, the general production of formaldehyde 

 when these substances resolve themselves under the influence of 

 light into simpler forms possesses a teleological bearing, for if in the 

 uptake of solar energy the first storage from the inorganic be in the 

 stage of formaldehyde, it would be very probable that in the process 

 of unbuilding this step should be retraced. 



The general production of formaldehyde by the action of light 

 on biochemical materials may also stand related to the important 

 lethal effects of sunlight and ultra-violet light upon micro-organisms, 

 which is seen in the sterilising action of sunlight upon many patho- 

 genic organisms and in the similar use of ultra-violet light installa- 

 tions for sterilisation purposes. 



The relationship of the lethal effects to the wave-length of 

 the light has been studied by many observers. Downes and Blunt 2 

 showed, at an early period, not only that both direct and diffuse 

 sunlight inhibited the appearance and slowed the growth of organisms 

 self-sown in Pasteur's cultivation fluid, but that this action did not 

 appear when the cultures were preserved behind red or yellow 

 glass screens, while blue or violet glasses allowed light to pass which 

 possessed as much deterrent action as light through clear glass. 

 Marshall Ward 3 was the first to invent an ingenious method of making 



1 Roy. Soc. Proc., B, vol. Ixxxix., p. 342 (1916). 



2 Roy. Soc. Proc., vol. xxvi., p. 488 (1877); vol. xxviii., p. 199 (1879). 



3 Roy. Soc. Proc., vol. liv., p. 472 (1893); other papers by Marshall Ward 

 on this subject, Roy. Soc. Proc., vol. lii., p. 393 (1892); vol. liii., pp. 26 and 

 164 (1893); vol. Ivi., p. 345 (1894). 



