92 FRAGMENTS OF SCIENCE 



as the crystal of salt or sugar. Many of the parts of the 

 body are obviously mechanical. Take the human heart, 

 for example, with its system of valves, or take the ex- 

 quisite mechanism of the eye or hand. Animal heat, 

 moreover, is the same in kind as the heat of a fire, be- 

 ing produced by the same chemical process. Animal 

 motion, too, is as certainly derived from the food of the 

 animal as the motion of Trevethyck's walking-engine 

 from the fuel in its furnace. As regards matter, the 

 animal body creates nothing; as regards force, it creates 

 nothing. Which of you by taking thought can add one 

 cubit to his stature? All that has been said, then, re- 

 garding the plant, may be restated with regard to the 

 animal. Every particle that enters into the composition 

 of a nerve, a muscle, or a bone has been placed in its 

 position by molecular force. And, unless the existence 

 of law in these matters be denied, and the element of 

 caprice introduced, we must conclude that, given the 

 relation of any molecule of the body to its environment, 

 its position in the body might be determined mathemat- 

 ically. Our difficulty is not with the quality of the prob- 

 lem, but with its complexity; and this difficulty might be 

 met by the simple expansion of the faculties we now pos- 

 sess. Given this expansion, with the necessary molecu- 

 lar data, and the chick might be deduced as rigorously 

 and as logically from the egg as the existence of Neptune 

 from the disturbances of Uranus, or as conical refraction 

 from the undulatory theory of light. 



You see I am not mincing matters, but avowing 

 nakedly what many scientific thinkers more or less dis- 

 tinctly believe. The formation of a crystal, a plant, or 

 an animal, is, in their eyes, a purely mechanical prob- 



