SOURCE OF OKGANIC ENERGY. 39 



may be compared with a hoop rolUng down an in- 

 clined plane, — if the stroke of a stick disturb its 

 balance, the hoop wabbles and the curves followed 

 by every point in the hoop are changed throughout 

 the rest of its course. In living matter, so long as 

 the chemical substances combine and separate in 

 constant, regular flow, and so long as no change 

 occurs in the forces acting upon the molecules, 

 there exists a steady mobile equilibrium. But let 

 there be at some point a little less heat or light, 

 and the conditions of chemical combination are 

 changed ; there may be a falling off in the assimi- 

 lation of some element, the composition of the 

 molecules is changed, and as a consequence they 

 assume a new configuration of oscillation, which 

 produces a new condition of strain affecting the mass, 

 and an almost endless series of effects ensue, the 

 chemical changes producing physical changes, and 

 vice versa. 



It is evident that the combinations of forces 

 which maintain living matter in its state of mobile 

 equilibrium must be exceedingly complex. Every 

 particle of living matter has its own peculiar mo- 

 tion in the body of an organism, now carried 

 along in circulating fluids, then perhaps deposited 

 in some appendage where it performs a great 

 variety of movement, and eventually it is cast off 



