HEAT, A MODE OF MOTION. 19 



to * bethei 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 a 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 as a peculiar mode of motion. The motion 

 of the hammer as it falls upon the anvil is not lost, but 



