HEAT, A MODE OF MOTION. 19: 
to whether it be internal or external to an organism, 
is, in other words, to affirm a miracle. If this is weighed 
against the physical view, “which in its perfection 
reduces every organic process to a problem of pure 
mechanics,” it may be done in the certainly impartial 
words of the naturalist just.quoted: “I am of opinion 
that the mechanical view of organic life is demonstrated 
only when all the motions in an organism are shown to 
be the effects of forces, which at other times also are 
inherent in the atoms. But similarly I should regard 
the vitalistic view as proved, if in any case a particular 
motion actually observed to take place in an organism 
were shown to be mechanically impossible. At pre- 
sent, neither is to be thought of. Nevertheless, if a 
decision must be made without full proof, I provisionally 
profess myself unequivocally in favour of the mechanical 
view. Not only does it recommend itself 4 priori by 
its superior probability and simplicity, but the progress 
of scientific development raises it almost to a certainty. 
When it is seen how certain phenomena—such as the 
‘evolution of animal heat, which it was formerly believed 
could be explained only by vital force—are now ascribed, 
even by those who in general assume the existence of 
a special vital force, to the universally active forces of 
the material particles, we find ourselves almost forced 
to the conviction that by degrees all the phenomena 
of life will become susceptible of mechanical explana- 
tion.” 
For the elucidation of the example just given of animal 
heat, let us observe that modern physics have learnt to 
know heat asa peculiar mode of motion. The motion 
of the hammer as it falls upon the anvil is not lost, but 
