GREATER PROBLEMS OF BIOLOGY—THOMPSON. 891 
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. [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 al! 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 leads some men, such as 
