ABNORMAL ANATOMY OF NERVES AND NER VOUS CENTRES.—The great space already occu pied by this article obliges me to compress into as small a compass as possible the observations which I propose to make under this head.
An interesting preliminary question is to de termine to what extent nervous matter is capa ble of being regenerated, when any solution of its continuity may have occurred. In nerve it has long been proved that such regeneration is capable of taking place. If the nerve be simply divided, without loss of substance, union may take place immediately ; but if a piece of it have been cut away, a considerable period must elapse before its complete restora tion. This was satisfactorily proved by Dr. Ilaighton's* experiments, in which he found that the function of the inferior laryngeal nerve in dogs was restored six months after division of the vagus, but with altered tones. Tiede mann divided in a dog the nerves of the fore foot and leg, and at the expiration of eight months observed that sensation and motion re turned ; after twenty-one months the sensi tive power had increased considerably, and at length the dog repined the complete use of his foot. Schwann divided both sciatic nerves of a frog, in the middle of both thighs : imme diately after the operation the frog's movements were very imperfect; after a month it had gained some power; but in three months it leaped as well as if no division had taken place. The sensibility of the foot, which was destroyed by the section, became nearly entirely restored ; and irritation of the nerve with a needle above the cicatrix produced strong contmctions in the muscles supplied from the nerve below the wound. On examination with the microscope, Schwann found that the cicatrix consisted of true nerve fibres disposed in their usual way.-l Miiller mentions the interesting fact of the return of some degree of sensation in the flaps of skin used for the Taliacotian operation for a new nose, as an argument in favour of the re production of nerves. Dieffenbach, however, who has had so much experience in these ope rations, states that the return of sensibility is only very imperfect, which is to be expected, since the divided extremities of the same fibres cannot re-join, except in very small number.
The evidence of restoration of function in divided nerves in the human subject is imper fect, although not opposed to what has becn above stated. Gruithuisen's observations on the consequences of an accidental division of the dorsal nerve of the thumb in his own per son are sufficiently conclusive. Eight months after the division, although the sensation had returned, it was so imperfect that the mind could form no conception of the precise point stimulated, as if the isolation of the fibres so necessary to exact sensation had been de stroyed in the cicatrix, or as if the fibres of the peripheral portion of the nerve had not unitetl with the corresponding ones in its central por tion. Mr. Earle relates a case in which a part of the ulnar nerve was cut out ; at the end of four years the little finger was useless, and the sensations very imperfect.
Indeed there is much difficulty in drawing conclusions from the restoration or non-restora tion of function after division of nerves, for no artificial disposition of the cut extremities will insure the corresponding fibres meeting. A sen sitive fibre may be joined to a motor, and thus the office of both would be neutralised ; or dif ferent sensitive fibres might unite, frona which doubtless some confusion, as to the nature and position of the impression would ensue.
The microscopic examinations of Seinruelt, Hermann, Nasse, and Klencke have rendered it certain that true nerve-fibres are reproduced in the cicatrix of a divided nerve. Nasse states that they are smaller than the natural size; and he has likewise pointed out an interesting fact, in the decrease of size of the fibres of the peripheral segment of the nerve as compared with those of the central segment, showing that a certain degree of atrophy takes place in that portion of the nerve, even after it has been se parated for a short period from its connection with the nervous centre. This author never saw sensation and motion return, although he kept the animals for three quarters of a year. Perhaps this was owing to his having removed large portions of the nerves lie operated npon.