264 On Modern Philosophical Conceptions of Life. 
and new. And [ also know that one of the chief character- 
istics of true science is the sharpness with which it enables us 
to discriminate between that which we have proven and really 
know and that which we have not proven and do not know. 
Better far is it, and a thousand times more in accord with the 
simple honesty of science, to acknowledge frankly the truth, 
that phenomena occur in living beings which the inorganic 
forces do not explain, than to mistake our wishes for disco- 
veries, to convert conjectures into dogmas, or, worst of all, to 
transform an undemonstrated hypothesis into a superstitious, 
ageressive, and intolerant creed. 
Nor will the soundness of the conclusions at which the 
present generation shall arrive as to this matter, be without 
its practical effect upon methods of biological research, and 
the consequent future progress of biological science. It is 
not a mere metaphysical subtlety, but a subject of practical 
importance, that I have asked you to consider to-night. For 
if the chemico-physical hypothesis of life be true, the only 
road of progress in biology lies through the chemical and 
physical laboratories. Now, I have already this evening 
more than once indicated how highly I esteem the class of 
biological work that has already been done in these labora- 
tories, and I have endeavoured to show how large is the un- 
explored biological field that can be explored only in this 
manner. But in addition to all that we can ever hope to do 
in this direction—and I insist upon its importance—l insist 
also upon the importance of other lines of work: I insist upon 
the importance of the systematic study of the phenomena of 
growth and development, of generation and heredity, of sen- 
sibility and mind. All that can thus be learned we need to 
know, and not merely for its own sake. ‘This knowledge is 
indispensable to the right interpretation of the succession of 
life upon the globe in the past, and the successful direction of 
the interference of the human will with the future succession of 
life upon the globe in accordance with human necessities. 
We shall make slow progress in this direction if we confine 
our efforts to the application of chemistry and physics to those 
phenomena of living beings that can be thus explained. The 
other phenomena, not thus explicable, must also be studied 
in detail, arranged into orderly groups, and made the basis of 
such inductions as our knowledge of them may warrant. It 
is only by pursuing this method that we can hope ultimately 
to acquire, with regard to the phenomena of living beings, 
that power to predict, which is the criterion of true science, 
and that power to control, which we so sorely need. 
