THE NERVOUS SYSTEM 301 



the other portion is regulcarly distributed, independently of the indi-vi- 

 dual's will, to those parts of the body which have to be kept incessantly 

 in action for the preservation of life. 



It would be highly inconvenient if the movements of our heart 

 or arteries, or the functions of our viscera or secretory or excretory 

 organs, were dependent on our will ; but it is equally important for 

 the satisfaction of all our requirements that we should have at our 

 disposal some portion of our nervous fluid, for despatching to the regions 

 that we wish to actuate. 



It appears that the nerves which continually convey the nervous 

 influence to the vital organs and to the muscles that are independent 

 of the individual, have a firmer or denser medullary substance than the 

 other nerves ; or have some other distinguishing peculiarity, as a result 

 of which not only does the nervous fluid move less rapidly and less 

 freely, but is also to a great extent protected from those general agita- 

 tions caused by the emotions of the inner feehng. If it were other- 

 wise, every emotion would interfere with the nervous influence necessary 

 to the essential organs and vital movements, and would endanger the 

 life of the individual. 



Those nerves, on the contrary, which convey the nervous influence 

 to the muscles dependent on the individual, allow to the subtle fluid 

 which they contain every hberty and rapidity of movement, so that the 

 emotions of the inner feeling easily set these muscles in action. 



Observation justifies us in the belief that the nerves which serve 

 for the excitation of muscular movement issue from the spinal cord 

 in vertebrates, from the ganglionic longitudinal cord in such inverte- 

 brates as have one, and from the separate ganglia in those which have 

 neither a spinal cord nor a ganglionic longitudinal cord. Now these 

 nerves, destined for muscular movement, have no close connection 

 with the sensitive system, in animals which have feeling, and when 

 they are injured they produce spasmodic contractions and do not 

 interfere with the system of sensations. 



Hence there are grounds for the belief that, of the various special 

 systems which compose the nervous system at its highest perfection, 

 that which is engaged in muscular excitation is distinct from that which 

 serves for the production of feeling. 



Thus the function of the nervous system, which consists in producing 

 muscular activity and the performance of the various vital functions, 

 can only be fulfilled by the dispatch of the subtle fluid of the nerves 

 from the reservoir to the various regions. 



But that other function of the nervous system which induces feeling 

 is of quite a different character ; for the production of a sensation 

 cannot occur without nervous influence, and it requires that the subtle 



