510 THE POPULAR SCIENCE MONTHLY. 



Now, there are no more perfect examples of closed systems wliicli 

 are the seat of constant motion than living beings, because life is 

 a type of never-ceasing co-ordinate changes. Can instances be 

 found in living beings ? What we have to look for is a reaction- 

 ary force, which not only opposes the generating stress by setting 

 up one like it and opposite in direction, but, furthermore, as the 

 change progresses it must tend to reduce the initial impulses which 

 created the change, this being what I have ventured to call the 

 new principle. 



Let us once more consider the case of muscular fatigue in the 

 light of this idea. The initial cause of muscular contraction is 

 the nervous stimulus sent to the organ. As soon as the muscle 

 contracts, the motion within it generates free acid. This acid, 

 which is therefore of the nature of a reactionary product, reduces 

 the irritability of the fibrillse, but, in addition, it reduces the 

 power of a nerve to transmit and to generate nerve force, so that 

 not only is the mandate traveling along the nerve resisted by the 

 greater sluggishness of the muscle, hut also the nerve force itself, 

 which is the material form taken by the will, is attacked and less- 

 ened in the very place of its origin. 



Is this not closely analogous to the cutting down of the electro- 

 motive force of the dynamo by the current which that same force 

 creates ? 



Another example, dealing with the chemical rather than the 

 mechanical force of the body, is found in digestion. Hunger is a 

 sensation which is probably the collective cry sent up from all 

 parts of the organism ; but the stomach and certain nerves seem 

 to be its principal seat. The irritability of a hungry man is a 

 well-known phenomenon. The exacerbation of many nervous 

 symptoms due to exhaustion is familiar to physicians. Hunger, 

 then, is an active, not a passive, state, and denotes that certain 

 changes of a positive kind are going on which tend to proceed to 

 the ultimate destruction of the animal if not checked. When 

 food enters the stomach and commences to be digested that organ 

 works harder, but the production of this labor taxes the forces of 

 the body by calling blood away from other organs ; in addition to 

 this, the nutriment given to the nerves stops the wasteful action 

 going on in them. So here, as in the previous cases, the reaction 

 set up cuts down the initial cause, and hunger vanishes. 



Many other instances might be drawn from physiology, but, 

 leaving them on one side, I desire to make a few suggestions con- 

 cerning that larger aggregate of life the social state. 



The warlike temperament of man has been one of his most 

 prominent characteristics from the earliest times. To live to fight 

 has been the chief aim of most primitive peoples, and has been a 

 leading occupation of all civilized ones. Armies have grown in 



