The rigid and contracted state of the muscles of paralysed limbs, which ftequently accompa nies red softening of the brain, arises from the propagation of the excited state of the diseased part of the brain to that portion of the spinal cord which is connected with it, and from vvhich the nerves of the paralysed parts arise. These nerves likewise participate in the irritation of the cord, and thus keep the inuscles in a state of continued active contraction. There is no organic lesion of the cord in these cases ; its state of excitement is dependent on the cerebral irritation, and disappears if the latter yields to the influence of remedial measures.
To a similar extension of cerebral irritation, although of a much briefer duration, the con vulsions of epilepsy raay be attributed. The brain becomes the seat of irritation, and this spreads to the whole or a part of the spinal cord and to the nerves which arise from it. In many instances of epilepsy the convulsions are limited to one half of the body, and this is espe cially the case where a chronic lesion exists in the brain and forms a focus of irritation, which is propagated only to one half (the opposite) of the cord.
Some substances exert a peculiar influence upon the spinal cord and throw it into a state of considerable polar exciternent. Strychnine. is the most energetic substance of this class. If a certain quantity of this drug be injected into the blood or taken into the stomach of an ani mal, a state of general tetanus will quickly. ensue, sensibility being either unaltered or son/.
what exalted. The slightest touch upon the surface of the body, even a breath of wind blown upon it, will cause a general or partial convulsive movement. The whole extent of the spinal cord is in a state of excitement, and even the inedulla oblongata may be involved in it, whence the closed jaws, the spasmodic state of the facial muscles, the difficult degluti tion. When this polar excitement is raised to its highest degree, the slightest mechanical sti mulus applied to any one point of the cord affects the whole organ and throws all the mus cles which it supplies into spasinodic contrac tion, just as the least stimulus to peripheral parts has the same effect.
It is a very interesting fact, which I have fre quently satisfied myself of by careful examina tion, that, however great the polar excitement may have been into which the cord has been thrown by strychnine, it exhibits no change of structure which can be detected by our means of observation. The nerve tubes and other
elements entering into the formation of the cord have preserved their natural appearance in all the cases which I have examined.
Opium has the effect of creating a similar state of polarity in the cord. This is most, con spicuous in cold-blooded animals ; it produces a similar effect in the warm-blooded classes, but in a much less degree. Hence there is an objection to the use of opium in large doses in cases of tetanus; and experience has shewn the inefficacy and the injurious influence of this drug when administered in large quantities. When the cord is in this state of excitement, a stimulus applied to one part rnay excite a re mote part of it with great facility.
The curious tendency already referted to, which the male frog has to grasp objects pre sented to them by his anterior extremities, is to be attributed in part to a spontaneous exaltation of the polar force of the cord which takes place at the copulating season, in the spring of the year, and which is associated with an extraor dinary developement of the papillary texture of the integument of the thumb.
This exaltation of the polar force of the cord, in connection with the generative function, is a paint highly worthy of the attention of the physiologist as offering some explanation of the sympathy which exists between different organs, between those even which are reinote frorn each other, during the rutting season, or during utero-gestation.
It is worthy of notice here that cold has a considerable influence in controlling' this polar state of the spinal cord, and of other nervous centres likewise. Ice applied along the spine, or the cold douche, may be frequently em ployed with great benefit in cases of muscular disturbance dependent on this polar state of the cord. It seems to me more than doubtful that many of those drugs which have the character of possessing a sedative influence upon the nervous system can be employed for this pur pose either with safety or advantage. This applies certainly to hydrocyanic acid and to opium in large doses ; animals poisoned by these substances become convulsed before death, and this denotes their tendency to exalt the polarity of the cord. Conium and bella donna, according to my experience, exercise the most beneficial inflnence of any of the sedative drugs, and I have found them very useful in restraining tbe cramps and startings in para plegic cases.