516 EQUILIBRATION. 



we see going on in every race, must necessarily go on. Since 

 increase of number cannot but continue until increase of 

 mortality stops it; and decrease of number cannot but con- 

 tinue until it is either arrested by fertility or extinguishes 

 the race entirely. 



§ 174. The equilibrations of those nervous actions 

 which constitute what we know as mental life, may be classi- 

 fied in like manner with those which constitute what we dis- 

 tinguish as bodily life. AVe may deal with them in the 

 same order. 



Each pulse of nervous force from moment to moment 

 generated, (and it was shown in § 86 that nervous currents 

 are not continuous but rhythmical) is met by coun- 

 teracting forces; in overcoming which it is dispersed and 

 equilibrated. When tracing out the correlation and equiva- 

 lence of forces, we saw that each sensation and emo- 

 tion, or rather such part of it as remains after the exci- 

 tation of associated ideas and feelings, is expended in 

 working bodily changes — contractions of the involuntary 

 muscles, the voluntary muscles, or both; as also in a cer- 

 tain stimulation of secreting organs. That the movements 

 thus initiated are ever being brought to a close by the oppos- 

 ing forces they evoke, was pointed out above ; and here it is 

 to be observed that the like holds with the nervous changes 

 thus initiated. Various facts prove that the arousing of a 

 thought or feeling, always involves the overcoming of a cer- 

 tain resistance : instance the fact that where the association 

 of mental states has not been frequent, a sensible effort is 

 needed to call up the one after the other; instance the fact 

 that during nervous prostration there is a comparative in- 

 ability to think — the ideas will not follow one another with 

 the habitual rapidity; instance the converse fact that at times 

 of unusual energy, natural or artificial, the friction of 

 thought becomes relatively small, and more numerous, more 

 remote, or more difficult connections of ideas are formed. 



