SPECIAL PHYSIOLOGY. 65 



Some of these occur in the tissue of the intestinal walls, in 

 the muscular structure of the heart, in the bronchi, etc. 

 (visceral or parenchymatous ganglions). 



By means of these numerous ganglions or clusters of nerve 

 globules, the sympathetic system seems to serve as a centre 

 of certain reflex actions, as it possesses fibres having centrif- 

 ugal, and others having centripetal, properties. The great 

 sympathetic has been considered the seat of all those nerve 

 phenomena more or less mysterious that have been embel- 

 lished with the name of sympathetic, and which we now call 

 reflex phenomena. It must, however, be remembered that 

 the great sympathetic is in no wise a system by itself; it 

 simply shares in the properties and functions of the medullary 

 system, and is associated with the latter. 



In fact, its nerve fibres and filaments are excitable to the 

 same agents as the spinal nerves, that is, to electricity and 

 chemical agents ; but the physiological excitant that we have 

 previously designated by the name of volition or will has no 

 effect upon this system ; consequently, the movements which 

 are produced in the department of the great sympathetic are 

 all involuntary. On the other hand, those movements re- 

 sulting from the artificial excitation of the nerve require a 

 definite amount of time for their production. They are 

 manifested slowly and cease slowly. This new difference 

 has the same relation to the peculiar nature of the nervous 

 and sympathetic fibres as in the case of the fibres of Remak 

 (pp. 25 and 26), and of the muscles to which they are 

 distributed (smooth muscles ; see farther on). The exci- 

 tation of the filaments of the great sympathetic gives also 

 origin to the phenomena of sensibility, but an intense as well 

 as long-continued irritation must be brought to bear upon 

 them. In the pathological conditions the great sympathetic 

 is much more excitable, and becomes both the seat and con- 

 d uctor of a large number of painful sensations. Formerly, too, 

 the independence of this nervous system in its relations to 

 the cerebro-spinal system was much exaggerated. It was 

 made to preside as a central organ over the functions of the 

 viscera in general, and more especially of those belonging to 

 nutrition. Experiments by Cl. Bernard demonstrate that the 

 sub-maxillary ganglion may serve as a centre for the salivary 

 secretion ; yet this result has lately been denied by Schiff. \. 



1 Man. Schiff, " Lecons sur la Physiologic de la Digestion," 

 Vol. L, 12th Le S on. 



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