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THE AMERICAN NATURALIST [Vol. LVI 



formation of formaldehyde, H.CO.H, from carbonic acid, 

 OH.CO.OH, with liberation of free oxygen, or, to put it 

 more simply, the direct union of the carbon atom of CO2 

 with a hydrogen atom of H2O; (2) the formation of 

 sugars from formaldehyde, and (3) the formation from 

 nitrites and formaldehyde of nitrogenous organic sub- 

 stances, are the most fundamental and characteristic re- 

 actions of organic life. It is true that light of such short 

 wave-lengths (A = 200/u./*) as were required in Baly's ex- 

 periments to synthesize formaldehyde does not occur in 

 sunlight as it reaches the earth to-day; but, as we shall 

 see later, the same author has shown that, in the presence 

 of certain substances known as photocatalysts, the reac- 

 tion can be brought about by ordinary visible light ; and 

 from Moore and Webster's work it appears that colloidal 

 hydroxides of uranium and of iron are suitable photo- 

 catalysts for the purpose. 



If these results of the pure chemist are justified, they 

 go far towards bridging the gap which has separated the 

 inorganic from the organic, and make it not too presump- 

 tuous to hazard the old guess that even to-day it is possible 

 that organic matter may be produced in the sea and other 

 natural waters without the intervention of living organ- 

 isms. We may note here, too, that if we take account of 

 only the most accurate and adequately careful work, the 

 actual experimental evidence at the present time requires 

 the presence of a certain amount of organic matter in the 

 culture medium or environment before the healthy growth 

 of even the simplest vegetable organism can take place. 

 This was illustrated in some experiments made by myself 

 some years ago when attempting to grow a marine diatom, 

 Thalassiosira gravida, in artificial sea-w^ater made up 

 from the purest chemicals obtainable dissolved in twice- 

 distilled water. Even after nutritive salts, in the form 

 of nitrates and phosphates, had been added, little or no 

 growth of the diatom occurred. But if as little as 1 per 

 cent, of natural sea-water were added, excellent cultures 

 resulted, in which the growth was as healthy and vigor- 

 ous as I was able to obtain when natural sea-water was 



