Action of Light Hays on Organic Compounds. 185 



as shown by Marshall Ward, is the most universal and potent natural 

 purifier of our oceans and streams and our supplies of drinking-water. 

 Light is also the agency which in spring, when the sun attains a certain 

 altitude and less of the actinic light is absorbed by the atmosphere, 

 penetrates the water of the ocean and lakes in sufficient intensity to 

 stimulate the great oiitburst of vegetable plankton, which initiates the long 

 sequence of swarms of animal life up to the fishes, and supports all the life 

 of the seas. This is evident, because the spring outburst of floating plant life 

 occurs before there has been any rise in the temperature of the sea-water. 

 The bronzing of the skin, caused by exposure to bright sunshine, and the 

 pigmentation of human races in tropical climates, is almost certainly a 

 protective screen against these injurious rays, and Marshall Ward has 

 pointed out that the pigments of those micro-organisms and fungi which 

 can flourish in light always absorb these injurious rays, and allow passage to 

 the reds, greens, yellows, and oranges, which are not injurious Even blue 

 and violet pigments occurring in nature, when carefully examined spectro- 

 scopically, are found in many cases to absorb the violet and shorter-waved 

 blues. 



The same is true of the colours of flowers, and even of the green colouring 

 matters of the foliage leaves, and it may well be that the function of the 

 chlorophyll, which usually occurs as a thin layer like a skin over the 

 chloroplast, is to temper and screen the light for the really effective 

 transformer lying underneath. 



The absence or great diminution of the blue and ultra-violet rays in hazy 

 or sunless weather may also be of great importance in allowing the disease 

 organisms of the higher plants to flourish unchecked, and it is such weather 

 in autumn which often heralds the outbreak of disease and blights. 



Summari/, 



The results are recorded under three sections : — (a) photo-synthesis by 

 inorganic transformers ; (b) action of sunlight and of ultra-violet light upon 

 concentrated solutions of formaldehyde ; (c) the general formation of form- 

 aldehyde by the action of light upon organic substances of bio-chemical origin. 



In the first section, the reactions of a number of inorganic systems in 

 presence of carbon dioxide and exposure to light are investigated, and it is 

 shown that certain of these can build up formaldehyde while others are inert. 

 The activity is shown to be related to the development of an optimum degree 

 of colloidality, and is not due to formation of higher or lower oxides, but 

 more probably to surface condensation on interfaces. 



The second section deals with the condensation of formaldehyde to form 



