PHYSIOLOGICAL 309 



extended, but Baly has apparently approached the confines of living 

 matter without using any material or means not readily available 

 in Nature. With the help of light he synthesised nitrogenous carbon 

 compounds from carbon dioxide and water and nitrites. May not 

 all this be at least peeping through a chink in the door which has 

 so far shut out from us the mystery of abiogenesis ? 



The twofold story — of diminishing carbon dioxide and increasing 

 oxygen — is thus nothing short of that of the evolution of the atmo- 

 sphere. This did not escape the speculative mind of Kelvin half a 

 century ago or more; but it does not seem to have been carried 

 much further. Geology, in its widest aspects, has of course almost 

 from its beginnings been considering not only the earth's solid 

 crust, and this as early formed upon a cooling but still unsettled 

 world, but also the significance of its waters, and in their circulation 

 from oceans and seas, and of their evaporating and condensing 

 water-vapour by rain, whence rivers, and these denuding and 

 sculpturing the older rocks as they descend, so ever laying down 

 new strata in the sea, and towards their varied upheavals. But the 

 earlier question is that of the withdrawal of oxygen from the primi- 

 tive atmosphere of our planet, as by its union not only with most 

 of the available hydrogen as water, H2O, and with carbon for 

 CO2; and, above all, by its formation of the primitive crust, by 

 union with the accessible metals, which earth- weighing experiments 

 have long shown to have been predominant in its mass from its 

 beginnings. When the world was thus crusted over, and thence 

 superficially cooled, enough for the precipitation of water-vapour, 

 the oceans would arise; hence leaving an atmosphere mostly of 

 passive nitrogen, with much carbon dioxide and water-vapour, but 

 with little oxygen left uncombined. Here, then, were conditions 

 more favourable for the beginnings of plant-life than for animal, 

 and this presumably aquatic, but in simpler forms than any we 

 know or can imagine ; yet with increasing contribution of oxygen as 

 its waste-product. With this enrichment of the atmosphere in 

 oxygen, animal-life could not but be aided and intensified — so on 

 such long-continued lines of atmospheric changes can we avoid 

 seeing a dual action on life in its evolution? It has often been 

 pointed out that the exuberant vegetation which has given us our 

 coal-beds suggests a moist atmosphere, rich in CO2. Yet the objection 

 arises — why not coal in earlier strata? since even by Carboniferous 

 times life was immemorially old, and something of moist land 

 conditions must surely have existed long before that period. Here, 

 as so often, the imperfection of the geological record still bafifles us 

 (though graphite deposits may be thus explained) ; yet all the more 

 such questions must be kept in view. The vivid and well-argued 

 hypothesis of Rene Quinton — that the lower specific gravity of the 

 fluids of land animals, as compared with sea-water (which is, of 



