SYMPATHETIC NERVE. 



467 



by Dupuy, on the other hand, it was de- 

 scribed as the immediate consequence of the 

 same. Reid found in his experiments that 

 the contraction of the pupil invariably takes 

 place in the dog and cat, but in the rabbit 

 the result is not so constant. Reid also 

 showed that it was not the section of the 

 trunk of the vagus, but that of the sympa- 

 thetic, that was the cause of the contracted 

 state of the pupil. According to Valentin 

 the effects produced differ considerably in 

 different animals : in the dog the pupil be- 

 comes very much contracted : the contraction 

 is not immediate, but ensues within about 

 half a minute after the nerve has been di- 

 vided. Stimulus applied to the nerve still 

 causes the pupil to dilate, but in a few mi- 

 nutes it again contracts, until it is not larger 

 than the head of a pin, and remains so for 

 months. The contracted pupil has generally 

 a circular form ; there are, however, occa- 

 sionally seen particular inequalities in its 

 margin which change from time to time. 

 When belladonna is applied the contracted 

 pupil dilates, but does not reach the size 

 which the sound pupil attains under similar 

 circumstances. When the aqueous humour 

 is tapped the contracted pupil becomes 

 slightly widened, while at the same time it 

 assumes a longish round form. In the sound 

 eye when treated in this way the pupil be- 

 comes diminished in size. 



Biffi found that slight dilatation of the 

 pupil followed irritation of the ascending or 

 carotid branches of the sympathetic, division 

 of these being also followed by contraction 

 of the pupil, though to a less extent than 

 takes place after division of the sympathetic 

 cord in the neck. Irritation of the superior 

 cervical ganglion gives rise to the greatest 

 dilatation of the pupil; so also when the same 

 is extirpated the contraction of the pupil is 

 very great. 



A number of researches have recently been 

 made, in regard to this subject, by Budge* 

 and Waller. When the stimulus of the mag- 

 neto-electric apparatus is applied to any part 

 of the sympathetic cord in the neck, dilata- 

 tion of the pupil takes place ; the part of the 

 nerve nearer the chest being, however, less 

 irritable than that higher up. The superior 

 cervical ganglion is not only more susceptible 

 of the stimulus than any other part of the 

 nerve, but the effect produced upon the pupil 

 also lasts longer. The dilatation of the pupil 

 may be produced by the application of the 

 galvanic stimulus to any part of the sympa- 

 thetic, from the inferior cervical ganglion to 

 the ophthalmic ganglion. Irritation of the 

 sympathetic below the inferior cervical gan- 

 glion, however, has no effect upon the pupil. 

 As regards the origin of the fibres in the 

 sympathetic which influence the pupil, they 

 might be supposed to proceed from three 

 sources: 1st. They might be regarded as 

 prolonged upwards from the thoracic portion 

 of the main cord, the inferior cervical gan- 



* See Budge, in Vierordt's Archiv. fur physio- 

 logisehe Heilkunde, 1852, Ergliuzungs Heft. 



glion being an organ interposed to prevent the 

 transmission of stimuli. Against this view, 

 however, there is the circumstance that the 

 fibres still pass through three ganglia before 

 they reach the eye, the superior cervical, 

 Gasserian, and ophthalmic. 2nd. The}' 

 might be supposed to arise in the inferior 

 cervical ganglion, or to be derived from the 

 spinal cord through the medium of the rami 

 communicantes. If they arise in the gan- 

 glion, the section of the sympathetic cord 

 below this, or of the branches which are con- 

 nected with the ganglion, ought not to give 

 rise to any contraction of the pupil, this de- 

 pending, according to Budge, upon the separa- 

 tion of the nerve-fibres from their centre. In 

 a dog which had been put under the influence 

 of chloroform, the inferior cervical ganglion 

 was sought, and the main cord of the sym- 

 pathetic below the ganglion, as well as all the 

 branches in communication with the latter, 

 were divided one by one. Of all these, only 

 one was found which acted on the pupil. 

 Division of this branch sometimes gave rise 

 to as decided contraction of the pupil as 

 division of the sympathetic cord in the neck. 

 In order to ascertain whether the branch in 

 question has its origin in the spinal cord, the 

 following experiment was made. A rabbit 

 was put under the influence of ether, and the 

 sympathetic of the left side divided in the 

 neck ; the spinal column was then opened 

 and the spinal cord cut across in the region 

 of the third dorsal vertebra, and galvanic 

 stimulus applied to the upper cut extremity 

 of the cord ; straightway the pupil of the 

 right side dilated, while that of the left side, 

 on which the sympathetic had been cut, did 

 not vary in the slightest. From further ex- 

 periments it was found that stimulus applied 

 to the spinal cord below the sixth dorsal ver- 

 tebra has no action on the pupil ; above this 

 point, however, and as high up as the fifth 

 cervical vertebra, dilatation was observed on 

 application of stimulus ; the portion of the 

 spinal cord which has most influence on the 

 pupil being that in the region of the first 

 three thoracic vertebrae. 



As regards the particular fibres in the sym- 

 pathetic on which its sensory and motor en- 

 dowments depend, Volkmann* believes that 

 none of the fine fibres, described by him as 

 sympathetic fibres, are possessed of sensory 

 properties in their normal condition. In 

 support of this view, he states, 1st. That the 

 number of these fibres is greatest in parts 

 which are least sentient, as is the case more 

 or less with all the organs of vegetative life, 

 and especially with the pia and dura mater, 

 and arachnoid, with the periosteum and with 

 the blood-vessels. The circumstance that 

 these parts are so very seldom, and some of 

 them never, the seat of impressions which 

 are transmitted to the sensorium, must, Volk- 

 mann observes, raise a suspicion that the very 

 rich network of nerve-fibres which occurs in 

 them are not possessed of sensory properties, 

 and the results derived from experiments, as 



* Loc. cit. p. 601. 



H H 2 



