Chap. TIL ACTION OF THE NERVOUS SYSTEM. 67 



lance, must be discussed at some little length; and it is 

 always advisable to perceive clearly our ignorance. 



The most striking case, though a rare and abnormal 

 one, which can be adduced of the direct influence of the 

 nervous system, when strongly affected, on the body, is 

 the loss of colour in the hair, which has occasionally 

 been observed after extreme terror or grief. One au- 

 thentic instance has been recorded, in the case of a man 

 brought out for execution in India, in which the change 

 of colour was so rapid that it was perceptible to the eye. 1 



Another good case is that of the trembling of the 

 muscles, which is common to man and to many, or 

 most, of the lower animals. Trembling is of no service, 

 often of much disservice, and cannot have been at first 

 acquired through the will, and then rendered habitual 

 in association with any emotion. I am assured by an 

 eminent authority that young children do not tremble, 

 but go into convulsions under the circumstances which 

 would induce excessive trembling in adults. Trembling 

 is excited in different individuals in very different de- 

 grees, and by the most diversified causes, — by cold to 

 the surface, before fever-fits, although the temperature 

 of the body is then above the normal standard; in 

 blood-poisoning, delirium tremens, and other diseases; 

 by general failure of power in old age; by exhaustion 

 after excessive fatigue; locally from severe injuries, such 

 as burns; and, in an especial manner, by the passage of 

 a catheter. Of all emotions, fear notoriously is the most 

 apt to induce trembling; but so do occasionally great an- 

 ger and joy. I remember once seeing a boy who had 

 just shot his first snipe on the wing, and his hands 



1 See the interesting- cases collected by M. G. Pouchet 

 in the ' Revue des Deux Mondes,' January 1, 1872, p. 79. 

 An instance was also brought some years ago before the 

 British Association at Belfast, 



