Nitrates in Aqueous Solution hy the Action of Sunlight. 159 



of light is that in which the synthesis of formaldehyde and carbohydrate is 

 effected in the green leaf, by that action of light upon water and carbon 

 dioxide in which the light-energy is converted into chemical energy and 

 stored up. 



It has been shown by Moore and Webster (1) that the first step, namely, 

 that of formaldehyde formation, in which the greatest upbuilding of molecules 

 with large storage of chemical energy occurs, can be effected by certain 

 catalysts, such as the ferric and uranium salts in colloidal solution in 

 water, when these are supplied with light-energy. Later, it was shown by 

 Moore (2) that such inorganic catalysts are present in the chloroplasts of 

 green cells. 



If it be agreed that life at some period first arose on this or some other 

 planet by a process of evolution from simpler constituents, it is clear that 

 there must have arisen along the path of evolution some combination or 

 mechanism for forming more complex molecules containing the elements 

 carbon, hydrogen, oxygen and nitrogen, from simpler inorganic substances 

 with a less content of energy. Otherwise, the substratum from which the 

 living organism was to be built could not exist, and there would have been 

 no store of existent chemical energy to act as nutriment for the simplest 

 living organism and supply the essential energy for the acts of life. 



The assumption that the green cell, with its complex structure and exceed- 

 ingly highly organised chemical substances, such as the chlorophylls, formed 

 at the dawn of life the first engine capable of utilising light-energy and 

 producing a gain of chemical energy is entirely untenable, and would make a 

 break in the continuity of inorganic and organic evolution, Such as nowhere 

 else is to be found. 



It hence becomes of great importance to study fully the action of light 

 upon those inorganic substances which are present in air and water, and might 

 be presumed, from their nature and present position as nutrients of living 

 organisms, to have been capable of being acted upon by light with inductance 

 of endothermic chemical reactions, and formation of more complex com- 

 pounds of organic character. 



Our knowledge of the first steps in the assimilation of both carbon and 

 nitrogen so as to take their part in the organic compounds is still very 

 incomplete, but that regarding nitrogen assimilation is much the more 

 fragmentary of the two. 



It is true that the living cell can by linkage of reactions utilise the energy 

 stored up in the form of carbohydrates, to induce endothermic reactions and 

 build up fats and proteins. As has been pointed out by Moore (3), a certain 

 amount of carbohydrates can be oxidised, and the energy so set free within 



o 2 



