384 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
between their machinery of pumps and pipes and reservoirs to the 
organs of the circulation of the blood, and since Vaucanson’s mar- 
velous automata lent plausibility to the idea of a ‘living automaton,” 
it is since then that men’s minds have been perpetually swayed by 
one or other of the two conflicting tendencies, either to seek an expla- 
nation of the phenomena of living things in physical and mechanical 
considerations, or to attribute them to unknown and mysterious 
causes alien to physics and peculiarly concomitant with life. And 
some men’s temperaments, training, and even avocations, render 
them more prone to the one side of this unending controversy, as the 
minds of other men are naturally more open to the other. As Kiihne 
said a few years ago at Cambridge, the physiologists have been found 
for several generations leaning, on the whole, to the mechanical or 
physico-chemical hypothesis, while the zoologists have been very 
generally on the side of the vitalists. 
The very fact that the physiologists were trained in the school of 
physics, and the fact that the zoologists and botanists relied for so 
many years upon the vague, undefined force of “heredity”’ as suffi- 
ciently accounting for the development of the organism, an intrinsic 
force whose results could be studied but whose nature seemed remote 
from possible analysis or explanation, these facts alone go far to 
illustrate and to justify what Kihne said. 
Claude Bernard held that mechanical, physical, and chemical 
forces summed up all with which the physiologist has to deal. Ver- 
worn defined physiology as ‘‘the chemistry of the proteids’”; and I 
think that another physiologist (but I forget who) has declared that 
the mystery of life lay hidden in ‘‘the chemistry of the enzymes.” 
But of late, as Dr. Haldane showed in an address a couple of years ago, 
it is among the physiologists themselves, together with the embryolo- 
gists, that we find the strongest indications of a desire to pass beyond 
the horizon of Descartes, and to avow that physical and chemical 
methods, the methods of Helmholtz, Ludwig, and Claude Bernard, 
fall short of solving the secrets of physiology. On the other hand, 
in zoology, resort to the method of experiment, the discovery, for 
instance, of the wonderful effects of chemical or even mechanical 
stimulation in starting the development of the egg, and again the 
ceaseless search into the minute structure, or so-called mechanism, of 
the cell, these I think have rather tended to sway a certain number of 
zoologists in the direction of the mechanical hypothesis. 
But on the whole, I think it is very manifest that there is abroad 
on all sides a greater spirit of hesitation and caution than of old, 
and that the lessons of the philosopher have had their influence on 
ourminds. We realize that the problem of development is far harder 
than we had begun to let ourselves suppose; that the problems of 
organogeny and phylogeny (as well as those of physiology) are not 
