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or on the ' stream-lines ' in the bodily form of fish or bird, from which the naval 

 architect and the aviator have learned so much. I admire that old paper of 

 Peter Harting'e in which he paved the way for investigation of the origin of 

 spicules, and of all the questions of crystallisation or pseudo-crystallisation in 

 presence of colloids, on which subject Lehmann has written his recent and 

 beautiful book. I sympathise with the efforts of Henking, Rhumbler, Hartog, 

 Gallardo, Leduc, and others to explain on physical lines the phenomena of nuclear 

 division. And, as I have said to-day, I believe that the forces of surface-tension, 

 elasticity, and pressure are adequate to account for a great multitude of the 

 simpler phenomena, and the permutations and combinations thereof, that are 

 illustrated in organic Form. 



I should gladly and easily have spent all my time this morning in dealing 

 with these questions alone. But I was loth to do so, lest I should seem to 

 overrate their importance, and to appear to you as an advocate of a purely 

 mechanical biology. 



I believe all these phenomena to have been unduly neglected, and to call for 

 more attention than they have received. But I know well that though we 

 push such explanations to the uttermost, and learn much in the so doing, 

 they will not touch the heart of the great problems that lie deeper than the 

 physical plane. Over the ultimate problems and causes of vitality, over what 

 is implied in the organisation of the living organism, we shall be left wondering 

 still. 



To a man of letters and the world like Addison, it came as a sort of revela- 

 tion that Light and Colour were not objective things but subjective, and that 

 back of them lay only motion or vibration, some simple activity. And when he 

 wrote his essay on these startling discoveries, he found for it, from Ovid, a 

 motto well worth bearing in mind, causa latet, vis est notissima. We may with 

 advantage recollect it, when we seek and find the Force that produces a direct 

 Effect, but stand in utter perplexity before the manifold and transcendent 

 meanings of that great word ' cause.' 



The similarity between organic forms and those that physical agencies are 

 competent to produce still leads some men, such as Stephane Leduc, to doubt or 

 to deny that there is any gulf between, and to hold that spontaneous generation 

 or the artificial creation of the living is but a footstep away. Others, like Delage 

 and many more, see in the contents of the cell only a complicated chemistry, and 

 in variation only a change in the nature and arrangement of the chemical con- 

 stituents ; they either cling to a belief in 'heredity,' or (like Delage himself) 

 replace it more or less completely by the effects of functional use and by 

 chemical stimulation from without and from within. Yet others, like Felix 

 Auerbach, still holding to a physical or quasi-physical theory of life,' believe that 

 in the living body the dissipation of energy is controlled by a guiding principle, 

 as though by Clerk Maxwell's demons; that for the living the Law of Entropy 

 is thereby reversed; and that Life itself is that which has been evolved to 

 counteract and battle with the dissipation of energy. Berthold, who first demon- 

 strated the obedience to physical laws in the fundamental phenomena of the 

 dividing cell or segmenting egg, recognises, almost in the words of John Hunter, 

 a quality in the living protoplasm, sui generis, whereby its maintenance, increase, 

 and reproduction are achieved. Driesch, who began as a 'mechanist,' now, as 

 we have seen, harks back straight to Aristotle, to a twin or triple doctrine of the 

 soul. And Bergson, rising into heights of metaphysics where the biologist, qua 

 biologist, cannot climb, tells us (like Duran) that life transcends teleology, that 

 the conceptions of mechanism and finality fail to satisfy, and that only ' in the 

 absolute do we live and move and have our being.' 



We end but a little way from where we began. 



With all the growth of knowledge, with all the help of all the sciences 

 impinging on our own, it is yet manifest, I think, that the biologists of to-day 

 are in no self-satisfied and exultant mood. The reasons and the reasoning that 

 contented a past generation call for re-inquiry, and out of the old solutions new 

 questions emerge ; and the ultimate problems are as inscrutable as of old. That 

 which, above all things, we would explain baffles explanation ; and that the 

 living organism is a living organism tends to reassert itself as the biologist's 

 fundamental conception and fact. Nor will even this concept serve us and suffice 

 us when we approach the problems of consciousness and intelligence and the 



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