SYSTEM OF THE GREAT SYMPATHETIC. 517 



and are, as a general rule, readily understood by the experimenter. 

 On the other hand, the principal part of the sympathetic system is 

 situated in the interior of the chest and abdomen ; and the mere 

 operation of opening these cavities, so as to reach the ganglionic 

 centres, causes such a disturbance in the functions of vital organs, 

 and such a shock to the system at large, that the results of these 

 experiments have been always more or less confused and unsatis- 

 factory. Furthermore, the connections of the sympathetic ganglia 

 with each other and with the cerebro-spinal axis are so numerous 

 and so scattered, that these ganglia cannot be completely isolated 

 without resorting to an operation still more mutilating and injuri- 

 ous in its character. And finally, the sensible phenomena which 

 are obtained by experimenting on the great sympathetic are, in 

 the majority of cases, slow in making their appearance, and not 

 particularly striking or characteristic in their nature. 



Notwithstanding these difficulties, however, some facts have been 

 ascertained with regard to this part of the nervous system, which 

 give us a certain degree of insight into its character and functions. 



The great sympathetic is endowed both with sensibility and the 

 power of exciting motion; but these properties are less active 

 here than in the cerebro-spinal system, and are exercised in a dif- 

 ferent manner. If we irritate, for example, a sensitive nerve in 

 one of the extremities, or apply the galvanic current to the poste- 

 rior root of a spinal nerve, the evidences of pain or of reflex 

 action are acute and instantaneous. There is no appreciable inter- 

 val between the application of the stimulus and the sensations 

 which result from it. On the other hand, experimenters who have 

 operated upon the sympathetic ganglia and nerves of the chest and 

 abdomen find that evidences of sensibility are distinctly manifested 

 here also, but much less acutely, and only after somewhat prolonged 

 application of the irritating cause. These results correspond very 

 closely with what we know of the vital properties of the organs 

 which are supplied either principally or exclusively by the sym- 

 pathetic; as the liver, intestine, kidneys, &c. These organs are 

 insensible, or nearly so, to ordinary impressions. We are not con- 

 scious of the changes and operations going on in them, so long as 

 these changes and operations retain their normal character. But 

 they are still capable of perceiving unusual or excessive irritations, 

 and may even become exceedingly painful when in a state of in- 

 flammation. 



There is the same peculiar character in the action of the motor 



