THE MECHANICAL CONCEPTION OF NATURE. 225 



it for moving the organs of his body, part of it in external 

 work. We can, therefore, compare him economically with 

 the efficiency of a steam-engine; it is only particular kinds 

 of fuel that you can give to him, ; but a loaf of bread and a 

 pound of beef will give you more work if used as food by 

 man, than if you had applied them to heat the boiler of a 

 small steam-engine. It is found that the activity of muscles 

 and nerves is dependent on a supply of blood containing 

 nutritious matter; that electrical phenomena are observed; 

 and that the muscular activity probably depends on a series of 

 explosions with oxidations, which may be compared to the 

 action of a set of minute gas-engines. The sense-organs and 

 nerves resemble very closely a system of telegraph wires 

 with their terminal key-boards. The semicircular canals and 

 organ of corti in the ear, though not yet fully explained, have a 

 correlation with the wave-lengths of sound ; and the eye 

 includes in itself a whole system of optics, its lens giving fine 

 exercise in determining focal lengths, with chromatic and 

 circular aberrations and corrections, and the retina, with its 

 rods and changing visual colours, suggesting that it must be 

 an instantaneous photographic camera. The victory of the 

 mechanical theory over these organs is only partial ; but all 

 the same it is significant. 



As might be expected, theory at this part has run ahead 

 of cliscoveiy. Some people venture to assert the mechanical 

 (or at least chemical) evolution of life from dead matter. In 

 ancient times it was the sceptics, like Lucretius, who denied 

 spontaneous generation. Christian teachers were rather dis- 

 posed to favour the idea of worms growing spontaneously 

 within human beings, of frogs being within trunks of trees 

 and rocks, of reptiles coming from the slime of the Nile. They 

 have latterly come to oppose this doctrine, and the most ad- 

 vanced scientific investigators agree with them in their oppo- 

 sition. Professor Huxley, when before the British Associa- 

 tion he threshed to death the theory of spontaneous genera- 

 tion, wound up with "an act of philosophical faith" that 

 after all, life may have arisen spontaneously in early geo- 

 logical times.* This would help him against the theists who 

 are continually tormenting him Avith their notions of the 

 necessaril}'- supernatural origin of life. Mechanism has not 

 yet explained how life began, anymore than hoAV matter and 

 energy began. So the theory is not entirely successful. 



* Brit. Ass. Rep., 1870, p. Ixxxiv. 



