146 THE HUMAN BODY. 



cease to be in communication with the nervous centre. 

 The movements they induce are then executed under the 

 influence of the nervous force pre-existing, and stored up irr 

 their substance. The great sympathetic gives motion and 

 sensation to the machinery of organic life; it controls the 

 nutritive functions, the circulation, the secretions, &c. 



Reflex power. Besides the voluntary movements which 

 result from the transmission of impressions by the nerves of 

 sensation, and from the perception of these impressions, 

 others are produced in which the will has no part, and which 

 result from the impulse directly reflected upon the motor nerves, 

 without any sensation having necessarily taken place, or at 

 least without our having any consciousness of it. These 

 are called reflex movements, and the force which determines 

 them, and is considered as peculiar to the nervous centre, is 

 called reflex power or the excito-motor faculty. Several physi- 

 ologists have considered the phenomena classed under the 

 name of recurrent sensibility as belonging to this reflex action, 

 but upon the origin of this sensibility authors are not agreed. 



Lastly, there is another reflex action which gives rise to 

 sympathy, that is the particular influence which certain organs 

 exercise upon others, such as the sensation called setting the 

 teeth on edge, produced by the grinding of metal against 

 stone or glass, and the sneezing provoked by tickling the 

 pituitary membrane, or by snuff, &c. (See Movements, p. 59.) 



Nervous force. The almost instantaneous transmission of 

 sensation and the motor impulse, by the different parts of 

 the nervous system, is one of the mysteries of the organism. 

 This class of phenomena has been compared to those pro- 

 duced in nature by electricity or magnetism, and the ques- 

 tion has been raised whether the nervous system is not 

 under the influence of an imponderable fluid produced in 

 its substance, or drawn from the same source as all the 

 elements of animate matter. Various names, such as nervous 

 fluid, nervous force, the active principle of the nerves, have 

 been given to the agent whose hypothetical existence permits 

 us to explain the nervous functions, as we explain the action 

 of the galvanic pile or the movements of the magnetic 

 needle. The admirable discovery of Galvani seemed to 



