September 30, 1922] 



NA TURE 



449 



cessful solution of this problem is defined physiologically 

 by the introduction of the conception ' kataholism.' 

 as implying that energy derived from the 'breaking 

 down ' of the plasma itself . . . may be regarded as 

 a ' secondary engine,' functional in the absence of 

 light, and evolved as a last resort in failing plasma." 

 Kataholism persists as the ultimate mechanism in the 

 physiology of animal as contrasted with plant life, but 

 if the suggestion just quoted is sound it originated, as 

 the first " adaptation " of the organism, to meet the 

 factor of recurring night and day. That the problem 

 was successfully solved we know, but as to the mechan- 

 ism of its solution we have no key. It is at this point, 

 again to use Church's words, that the "plasma, 

 previously within the connotation of chemical proteid 

 matter, becomes an autotrophic, increasingly self- 

 regulated, and so far individualised entity, to which 

 tin term ' life ' is applied." 



The elementary plasma is thus now fairly launched 

 as an individual living organism, and the great funda- 

 mental problems of biology — memory, heredity, varia- 

 tion, adaptation — face us at each step of our further 

 progress. We see in broad outline the conditions the 

 advancing organism had to meet, we see the means 

 by which those conditions were in fact met. we know 

 that only those individuals survived which were able 

 to meet them. Further than this we. the biologists 

 of to-day, have not advanced. The younger genera- 

 tion will pursue the quest, and, with patient effort, 

 much that now lies hidden will grow clear. 



The differentiation of the growing particles of plasma 

 into definite lavers. which followed, seems natural ; 

 first the external layer, in molecular contact with the 

 surrounding water, from which it receives substances 

 from outside in the form of ions, and to which it 

 itself gives off ions : beneath this the autotrophic 

 layer to which light penetrates, and in which, under 

 the influence of the light, new organic substance is 

 built up ; in the centre a layer to which light no longer 

 penetrates. This central region, the nucleus, depends 

 entirely on the peripheral layers for its own nutrition, 

 and becomes itself concerned only with katabolic pro- 

 cesses, those processes of the organism which depend 

 upon the breaking down, and not the building up, of 

 organic substance. 



Ai an early stage in the development of the in- 

 dividual organism the spherical shape, which the 

 organic plasma was compelled to assume under the 

 influence of surface-tension, underwent an important 

 modification, the effect of which has impressed itself 

 upoir all later developments. A spherical organism 

 floating in the water and growing under the direct 

 influence of light would obviously grow more rapidly 

 on the upper side, where the light first strikes it, than 

 it would on the lower side away from the light. There 

 followed, therefore, an elongation of the sphere in the 

 vertical direction, and the definite establishment of an 

 anterior end, the upper end which lay towards the 

 light and at which the most vigorous growth took 

 place. In tins way there was established a definite 

 polaritv, which has persisted in all higher organisms, 

 a distinction between an anterior and a posterior end. 

 With the concentration of organic substance which 

 took the form of nucleus and reserve food supply, the 

 specific gravity of the plasma would become greater 



NO. 2761, VOL. 1 IO] 



than that of the surrounding water and the organism 

 would tend to sink. The necessity, therefore, arose 

 for some means of keeping it near the surface, that 

 it might continue to grow under the influence of light. 

 The response to this need, however it was attained, 

 came in the development of an anterior flagellum. 

 This we may regard as an elongation in the direction 

 of the light of a contractile portion of the external 

 layer, moving rhythmically, which by its movement 

 counteracted the action of gravity, and acting as a 

 tractor drew the primitive flagellate upwards towards 

 the surface layers, into a position where further growth 

 was possible. With the establishment of the flagellum 

 an organ is produced which shows remarkable per- 

 sistence in both the animal and vegetable kingdoms, 

 and from the existence of the flagellated spermatozoon 

 in the higher vertebrates, in accordance with Haeckel's 

 biogenetic law that the individual in its development 

 repeats or recapitulates the history of the race, we 

 conclude that they also in their earliest history passed 

 through a plankton flagellate phase. 



Exactly at what stage in the history of the auto- 

 trophic flagellate the first formation of chlorophyll and 

 its allied pigments took place we have no means of 

 determining, but it may have been before even the 

 flagellum itself had begun. This advance and the 

 subsequent concentration of the pigments into definite 

 chromatophores or chloroplasts doubtless increased 

 immensely the efficiency of the organism in producing 

 the food which was necessary to it. The recent work 

 of Baly and his collaborators becomes here again of 

 the first importance, and though the subject of the 

 part played by chlorophyll in photosynthesis belongs 

 rather to botany and chemistry than to zoology. 1 

 may perhaps, for the sake of completeness, be allowed 

 to refer to it very briefly. I have already said that 

 Baly brought about the synthesis of formaldehyde 

 from carbon dioxide and water under the influence of 

 rays of very short wave-length (A = 2oo/i/x) from a 

 mercury-vapour lamp. He was also able to show that 

 when certain coloured substances were added to the 

 solution of carbon dioxide in water the same reaction 

 took place under the influence of ordinary visible 

 light. His explanation of this process is that the 

 coloured substance known as the photoeatalyst absorbs 

 the light rays and then itself radiates, at a lower infra- 

 red frequency corresponding to its own molecular 

 frequency, the energy it has absorbed. At this lower 

 frequency the energy thus radiated is able to activate 

 the carbonic acid, so that the reaction leading to the 

 formation of formaldehyde can and does take place; 

 In the living plant this synthesised formaldehyde 

 probably polymerises at once to form sugars. 



Malachite green and methyl orange, as well as other 

 organic compounds, were found to act as photocatalysts 

 capable of svnthesising formaldehyde, and Moore and 

 Webster's work had previously shown that inorganic 

 substances, such as colloidal uranium oxide and colloidal 

 ferric oxide, can do the same. Chlorophyll in living 

 plants may with some confidence be assumed to operate 

 in a similar way, though no doubt the series of events 

 is more complex, since the green pigment itself is not 

 a single pigment, and others, such as carotin and 

 xanthophyll, are also concerned. 



We have tried to picture the gradual building up 



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