78 FRAGMENTS OF SCIENCE 



muscular power. A horse can perform work, and so can 

 a man; but this work is at bottom the molecular work of 

 the transmuted food and the oxygen of the air. We in- 

 hale this vital gas, and bring it into sufficiently close 

 proximity with the carbon and the hydrogen of the body. 

 These unite in obedience to their mutual attractions; and 

 their motion toward each other, properly turned to ac- 

 count by the wonderful . mechanism of the body, becomes 

 muscular motion. 



One fundamental thought pervades all these state- 

 ments: there is one tap-root from which they all spring. 

 This is the ancient maxim that out of nothing nothing 

 comes; that neither in the organic world nor in the in- 

 organic is power produced without the expenditure of 

 power; that neither in the plant nor in the animal is 

 there a creation of force or motion. Trees grow, and 

 so do men and horses; and here we have new power 

 incessantly introduced upon the earth. But its source, 

 as I have already stated, is the sun. It is the sun that 

 separates the carbon from the oxygen of the carbonic 

 acid, and thus enables them to recombine. "Whether 

 they recombine in the furnace of the steam-engine or 

 in the animal body, the origin of the power they pro- 

 duce is the same. In this sense we are all "souls of fire 

 and children of the sun." But, as remarked by Helm- 

 holtz, we must be content to share our celestial pedigree 

 with the meanest of living things. 



Some estimable persons, here present, very possibly 

 shrink from accepting these statements; they may be 

 frightened by their apparent tendency toward what is 

 called materialism a word which, to many minds, ex- 

 presses something very dreadful. But it ought to be 



