Chap. III. ACTION OP TIIE NERVOUS SYSTEM. 71 



nied by consciousness. Why the irritation of a nerve- 

 cell should generate or liberate nerve-force is not known; 

 but that this is the case seems to be the conclusion ar- 

 rived at by all the greatest physiologists, such as Miiller, 

 Virchow, Bernard, &c. 6 As Mr. Herbert Spencer re- 

 marks, it may be received as an " unquestionable truth 

 that, at any moment, the existing quantity of liberated 

 nerve-force, which in an inscrutable way produces in us 

 the state we call feeling, must expend itself in some 

 direction — must generate an equivalent manifestation 

 of force somewhere; " so that, when the cerebro-spinal 

 system is highly excited and nerve-force is liberated in 

 excess, it may be expended in intense sensations, active 

 thought, violent movements, or increased activity of 

 the glands. 7 Mr. Spencer further maintains that an 

 " overflow of nerve-force, undirected by any motive, will 

 manifestly take the most habitual routes; and, if these 

 do not suffice, will next overflow into the less habitual 

 ones." Consequently the facial and respiratory mus- 

 cles, which are the most used, will be apt to be first 

 brought into action; then those of the upper extremi- 

 ties, next those of the lower, and finally those of the 

 whole body. 8 



An emotion may be very strong, but it will have 

 little tendencv to induce movements of any kind, if it 



6 Miiller (' Elements of Physiology,' Eng. translat. vol. 

 ii. p. 932) in speaking 1 of the nerves, says, " any sudden 

 change of condition of whatever kind sets the nervous 

 principle into action." See Virchow and Bernard on the 

 same subject in passages in the two works referred to 

 in my last foot-note. 



7 H. Spencer, ' Essays, Scientific, Political,' &c, Second 

 Series, 1863, pp. 109, 111. 



8 Sir H. Holland, in speaking (' Medical Notes and Re- 

 flexions,' 1839, p. 328) of that curious state of body called 

 the ftdpets, remarks that it seems due to " an accumula- 

 tion of some cause of irritation which requires muscular 

 action for its relief." 



