GREATER PROBLEMS OP BIOLOGY — THOMPSON. 391 



to mechanical considerations, to mathematical laws, or to physical 

 and chemical processes. 



I love to think of the logarithmic spiral that is engraven over the 

 grave of that great anatomist, John Goodsir (as it was over that of 

 the greatest of the Bernouillis) , so graven because it interprets the 

 form of every molluscan shell, of tusk and horn and claw, and many 

 another organic form besides. I like to dwell upon those lines of 

 mechanical stress and strain in a bone, that give it its strength 

 where strength is required, that Hermann Meyer and J. Wolff 

 described, and on which Roux has bestowed some of his most 

 thoughtful work; or on the kindred conformations that Schwendener, 

 botanist and engineer, demonstrated in the plant; or on the " stream- 

 lines" in the bodily form of fish or bird, from which the naval archi- 

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

 of Peter Harting's, in which he paved the way for investigation of 

 the origin of spicules, and of all the questions of crystallization or 

 pseudocrystallization in presence of colloids, on which subject 

 Lehmann has written his recent and beautiful book. I sympathize 

 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, 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 might well have devoted this essay to these questions, and to 

 these alone. But I was loath 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 we shall 

 be left wondering still. 



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

 of revelation that light and color 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 trans- 

 cendent meanings of that great word cause. 



The similarity between organic forms and those that physical 

 agencies are competent to produce still kads some men, such as 



