MATTER AND FORCE. 91 



motion produced in the act of union may be turned to 

 mechanical account. Passing from dead matter to living ^ 

 matter, we find that the source of motive power here re- 

 ferred to is also the source of muscular power. A horse 

 can perform work, and so can a man, but this work is at 

 bottom the molecular work of the elements of the food and 

 the oxygen of the air. We inhale this vital gas, and bring 

 it into sufficiently close proximity with the carbon and the 

 hydrogen of the food. They unite in obedience to their 

 mutual attractions, and their motion toward each other, 

 properly turned to account by the wonderful mechanism of 

 the body, becomes muscular motion. 



One fundamental thought pervades all these statements : / 

 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 inorganic is power 

 produced without the expenditure of other 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. For he it is who separates the carbon from the oxy- 

 gen of the carbonic acid, and thus enables them to recom- 

 bine. Whether they recombine in the furnace of the 

 steam-engine or in the animal body, the origin of the power 

 they produce is the same. In this sense we are all " souls 

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

 Helmholtz, we must be content to share our celestial 

 pedigree with the meanest living things. The frog, and 

 the toad, and those terrible creatures, the monkey and {/ 

 the gorilla, draw their power from the same source as 

 man. . 



Some estimable persons, here present, very possibly 

 shrink from accepting these statements ; they may be 

 frightened by their apparent tendency toward what is called 



