SYSTEM OF THE GREAT SYMPATHETIC. 523 



the circular fibres only, division of the sympathetic would be 

 followed by exclusive paralysis of the dilators, and a permanent 

 contraction of the pupil would consequently take place. The 

 above explanation, however, is not a satisfactory one; since, in 

 the first place, division of the oculo-motorius, as the experiments of 

 Bernard have shown, 1 does not by itself produce complete dilata- 

 tion of the pupil ; and, secondly, after division of the sympathetic 

 nerve in the cat, as we have already shown, not only is the pupil 

 contracted, but both the upper and lower eyelids and the nictitating 

 membrane are also partially drawn over the cornea, and assist in 

 excluding the light. The last-named effect cannot be owing to any 

 direct paralysis, from division of the fibres of the sympathetic. It 

 is more probable that the section of this nerve operates simply by 

 exaggerating for a time the sensibility of the retina, as it does that 

 of the integument ; and that the partial closure of the eyelids and 

 pupil is a secondary consequence of that condition. 



It will be remembered that in describing the inflammation of the 

 eyeball, consequent upon section of the fifth pair of nerves, we 

 found that there were reasons for believing this effect to be due 

 to injury of certain sympathetic fibres which accompany the fifth 

 pair. If the fifth pair in fact be divided at the level of the Cas- 

 serian ganglion, where it is joined by sympathetic fibres from the 

 carotid plexus, or between this ganglion and the eyeball, a destruc- 

 tive inflammation of the organ follows. But if the section be made 

 behind the ganglion, so as to avoid the filaments of communication 

 with the sympathetic, no inflammatory change takes place. If this 

 fact be really owing to the presence of sympathetic fibres which 

 accompany the fifth pair, it indicates a remarkable difference in the 

 effects of dividing the sympathetic near the eyeball and at a dis- 

 tance from it; since no real inflammation of the eyeball or its 

 appendages is ever produced by division of this nerve in the middle 

 of the neck, but only the elevation of temperature and increase of 

 sensibility which have been already described. 



The influence of the sympathetic nerve and the consequences 

 of its division upon the thoracic and abdominal viscera have been 

 only very imperfectly investigated by experimental methods. It 

 undoubtedly serves as a medium of reflex action between the sensi- 

 tive and motor portions of the digestive, excretory, and generative 



1 Lemons sur la Physiologie et U Pathologie du Sy?teoie Nerveux, Paris, 1858, 

 vol. ii p. 203. 



