Chap. III. ACTION OF THE NERVOUS SYSTEM. 75 



ous organs, in nearly the same manner as does great bod- 

 ily suffering. 



The heart no doubt will likewise be affected in a direct 

 manner; but it will also in all probability be affected 

 through habit; and all the more so from not being 

 under the control of the will. We know that any great 

 exertion which we voluntarily make, affects the heart, 

 through mechanical and other principles which need 

 not here be considered; and it was shown in the first 

 chapter that nerve-force flows readily through habitu- 

 ally used channels, — through the nerves of voluntary 

 or involuntary movement, and through those of sen- 

 sation. Thus even a moderate amount of exertion will 

 tend to act on the heart; and on the principle of asso- 

 ciation, of which so many instances have been given, 

 we may feel nearly sure that any sensation or emotion, 

 as great pain or rage, which has habitually led to much 

 muscular action, will immediately influence the flow of 

 nerve-force to the heart, although there may not be at 

 the time any muscular exertion. 



The heart, as I have said, will be all the more readily 

 affected through habitual associations, as it is not under 

 the control of the will. A man when moderately angry, 

 or even when enraged, may command the movements of 

 his body, but he cannot prevent his heart from beating 

 rapidly. His chest will perhaps give a few heaves, and 

 his nostrils just quiver, for the movements of respiration 

 are only in part voluntary. In like manner those mus- 

 cles of the face which are least obedient to the will, 

 will sometimes alone betray a slight and passing emo- 

 tion. The glands again are wholly independent of the 

 will, and a man suffering from grief may command 

 his features, but cannot always prevent the tears from 

 coming into his eyes. A hungry man, if tempting food 

 is placed before him, may not show his hunger by any 



