FUNCTIONS OF THE SYMPATHETIC SYSTEM. 737 



facts : In the first place, section or irritation of the spinal cord and certain of the en- 

 cephalic centres is capable of influencing the vaso-motor system, a fact which will he dwelt 

 upon more fully in another connection. In the second place, the experiments of Bernard 

 upon the submaxillary ganglion and its influence on the secretion of the submaxillary 

 gland have demonstrated, in the most conclusive manner, that this ganglion is the centre 

 presiding immediately over the reflex phenomena of secretion by the gland ; but it has 

 also been shown that, when all of the connections of the submaxillary ganglion with the 

 cerebro-spinal system are divided, after a few days, this ganglion loses its power as a 

 reflex nervous centre. In the chapters upon secretion, we have given numerous examples 

 of reflex action through the sympathetic system. The experiments just cited from Ber- 

 nard show that individual ganglia belonging to this system may act independently for a 

 time, but that this action cannot continue indefinitely, after the cerebro-spinal branches 

 have been divided. It remains, however, to apply these experiments to other sympa- 

 thetic ganglia ; but, in the case of the submaxillary, they are very satisfactory, from the 

 facility with which the parts may be operated upon and the certainty with which the 

 ganglion may be separated from its connections with the cerebro-spinal system. As 

 regards the explanation of the final loss of power over the functions of the submaxillary 

 gland, the experiments of Waller seem to have escaped the attention of the eminent 

 physiologist whom we have quoted. There is no experimental fact more conclusively 

 demonstrated than that of the anatomical degeneration and consequent loss of physio- 

 logical function of nerve-fibres in a few days after they have been separated from their 

 centres of origin. After division of a cerebro-spinal nerve-trunk, the tubes soon lose 

 their anatomical characters and will no longer respond to a galvanic stimulus. In the 

 case of the fibres operating upon the submaxillary gland, the question of their degenera- 

 tion after division of the cerebro-spinal roots was not submitted to microscopical investi- 

 gation. If these fibres had undergone the degeneration which has so frequently been 

 observed in experiments upon other nerves, their galvanization would not have produced 

 any effect ; which was precisely the result obtained by Bernard. In the absence of 

 direct observations upon this point, it is the most reasonable view to adopt, that the 

 fibres from the cerebro-spinal nerves had lost their function, as a natural consequence of 

 separation from their centres, and that this was the cause of the absence of effect upon 

 the gland following their galvanization. The observation of Bernard shows, however, 

 that filaments may pass to special organs from the cerebro-spinal centres through the 

 sympathetic ganglia. 



Functions of the Sympathetic System. 



In the early part of the last century (1712 and 1725), Pourfour du Petit demonstrated 

 that the influence of the sympathetic nerve in the neck (the great sympathetic was fre- 

 quently called the nervus intercostalis) was propagated from below upward toward the 

 head, and not from the brain downward. This may be taken as the starting-point of our 

 definite knowledge of the functions of the sympathetic system, though the experiments 

 of Petit showed only the influence of the cervical portion upon the eye. In 1816, Dupuy 

 removed the superior cervical ganglia in horses, with the effect of producing injection of 

 the conjunctiva, increase of temperature in the ear, and an abundant secretion of sweat 

 upon one side of the head and neck. These experiments showed that the sympathetic 

 has an important influence upon nutrition, calorification, and secretion. In 1851, Bernard 

 repeated the experiments of Pourfour du Petit, dividing the sympathetic in the neck on 

 one side in rabbits, and noted, on the corresponding side of the head and the ear, in- 

 creased vascularity, and an elevation in temperature, amounting to from 7 to 11 Fahr. 

 This condition of increased heat and vascularity continues for several months after divi- 

 sion of the nerve. In 1852, Brown-SSquard repeated these experiments and attributed 

 the elevation of temperature directly to an increase in the supply of blood to the parts 

 affected. He made a most important advance in the history of the sympathetic, by 

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