A number of researches have recently been made, in regard to this subject, by Budge* and Waller. When the stinmlus 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 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. They 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 s3 m 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 stiniulus 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 vvas 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 vertebrw.
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 well as from surgical operations, would seem to show that such is the case. The coats of the blood-vessels he considers to be destitute of sensibility, inasmuch as he found that the operation of fixing the hmma-dynamometer into them gave rise to no distinct sign of pain. 2nd. As regards the fibres which take their origin from the ganglia, it seems in a high degree probable that they at least cannot convey impressions from the organs which they supply to the sensorium. In order to communicate such impressions they must transfer them to fibres which do not terminate in the ganglia, but are directly or indirectly connected with the sensorium, and are, in short, true sensory fibres. Such a trans ference in the normal condition does not, howaver, appear to take place. 3rd. It is not at all probable that fibres, which in ani mals that have been beheaded, or are under the influence of strychnine, show so little connection with the spinal cord that: stimulus applied to them cannot excite any reflex movements in the voluntary muscles, should be in a condition to communicate impressions through the spinal cord to the sensorium. 4th. Division of the cerebro-spinal nerves which supply the integument is followed by loss of sensibility in that part, although the sympathetic fibres passing to the same have been left uninjured. In the frog, a great number of fibres are sent from the sympathetic to the cerebro-spinal nerves, and are along with these distributed in considerable quantity to the integument : if now the nerves in the leg of the frog be divided above the point at which the fibres of the sympathetic join them,so as in this way to leave the continuity of the latter unin jured, the limb is notwithstanding deprived of sensibility ; the power of exciting reflex action in the muscles of the limb by stimulus applied to the integument being also at the same time destroyed. Division of the fifth nerve, in like manner, is attended by loss of sensibility in all the parts of the face supplied by this nerve ; and no reflex action can be excited by stimulus applied to the eye, tongue, &c., al though these parts derive fibres from the sympathetic, which are not divided in the operation. Although in the normal condition the fibres in question are not capable of com municating impressions to the sensorium, they may, however, according to Volkmann, do so in diseased states. In this way the severe pain which is sometimes felt in organs sup plied by the sympathetic, does not depend so much on cerebro-spinal nerve-fibres as on an altered condition of the ganglionic fibres themselves. The number of cerebro-spinal fibres distributed to such parts is too small to explain it. Severe pain is frequently felt in bones when diseased, although, according to Volkmann, these probably receive none but sympathetic filaments. The circumstance already mentioned, that in experimenting on the sensibility of the ganglia, it has been found that these are frequently incapable of trans mitting impressions until by frequent irrita tion they have been brought into a kind of inflammatory condition, also indicates the same thing.