These doctrines are repeated and somewhat enlarged upon in a much later work by Pro chaska, published at Vienna in 1810, entitled, " Lehrsitze aus der Physiologie des Men schen," a third and intich enlarged edition of a text book for his lectures. The whole section on the nervous system will repay an attentive perusal, and especially the chapter headed " Verrichtung des allgemeinen Sensoriums," which contains a review of the doctrine of re flex actions. A later edition of the same work, somewhat compressed in some parts, published in 1820, contains a repetition and a distinct enunciation of the same doctrines (p. 92).• It is not a little reniarkable, and at the same time highly discreditable to physiologists, that views so comprehensive and so striking shonld have been suffered to fall into neglect and to be come almost wholly forgotten, and that the pe culiar power of nervous centres to develope motions in response to sensorial impressions, or, in Prochaska's language, " to reflect sensorial into motor impressions," should lifth been lost sight oE Le Gallois, indeed, had recognized this power, and Diane had evidently much insight into it; Mayo, likewise, had formed a very correct appreciation of it; as shown by his observations on the actions of the iris. But none of these physiologists were fully impressed with its immense importance. It is to Dr. Marshall Hall in this country and to Professor Midler in Germany that science is most in debted for awakening the attention of physi ologists to the existence of a power in the nervous centres which no doubt exercises a wide influence on the phenomena of living creatures ; and yet it seems extraordinary that neither of these physiologists in their earlier writings should have made the slightest allusion to Prochaska, wit° had offered a more precise and more comprehensive, and, as I hope to show, a truer explanation of the phenomena than either of them.
I shall here cite various facts. in addition to those already adduced, which unequivocally demonstrate that a power exists in the cord of exciting movements in parts which receive nerves from it, by changes occurring in its substance, which may arise there from some modification of its nutrition developed in the cord itself, or be excited by a stimulus brought to act upon it by afferent or sensitive nerves.
But more than this : the cord has the power of reflecting the change wrought in it by im pressions conducted to it into adjacent sensi tive nerves, thus creating a large class of reflex phenomena under the name of reflex or radia ting sensations.
When a stimulus is applied to the spinal cord, either directly or through the medium of afferent nerves, the actions excited by it are generally limited to those parts which derive their nerves from that segment of the cord which has received the stimulus. In some instances, however, parts supplied from other and even distant segments are thrown into action. Thus irritation of one leg may cause movements of one or both of the upper extremities ; the intro duction of a catheter into the urethra svill some times give rise to forcible contractions of the muscles of the lower extremities or even of all the limbs. These effects are due, no doubt, to
the extension of the stimulation in the cord be yond the point first acted upon ; and they may be regarded as proofs that that peculiar state of physical change which nervous stimulation can excite in a centre may be propagated in the spinal cord upwards, downwards, or sideways, fmm the seat of the primary stimulation.
This fact was pointed out first, so far as I know, by Dr. 111. Hall, who regards it fIS a property of the cord in its normal state. This, I am inclined to think, is an error; I believe it to be a property of the cord, only when its polarity is exalted. It is, however, an important property, and we shall, by-and-bye, make use of it in considering the mechanism of the various actions of nervous centres. Meantime we inay obtain, from examining into the morbid states which are apt to arise in the spinal cord and in other parts of the cerebro-spinal centres, in teresting confirmation of it.
A wound in the sole of the foot or ball of the thumb, or in some other situation favourable to the maintenance of prolonged irritation, is ca pable of exciting a particular region of the cord, from which the state of excitement spreads so as to involve not only the whole cord, but part of the medulla oblongata also ; and in this state a large proportion of the motor nerves participate, so as to induce tonic contraction of the muscles they supply. This is the rationale of the developement of that fearful malady called tetanus. It consists not in an inflam ma tory condition of the cord or of its membranes, nor in congestion of them, but simply in a state of prolonged physiml excitement, the natural polar force of the centre being greatly exalted and kept so by the constant irritation propagated to it by the nerves of the wounded part. Intestinal irritation is capable of pro ducing a similar condition which, if the irrita tion have not been allowed to remain too long, inay be speedily removed by getting rid of the irritating cause. The following case illustrates this : an unhealthy looking girl, about fifteen years of age, was brought into King's College Hospital suffering from severe tonic spasms of the muscles of the spine and lower extremities. The spasms were so powerful as to produce successive paroxysms of opisthotonos, during which the trunk became bent like a bow, so that the patient rested on her occiput and on her heels. This state was speedily removed by the use of a large purgative clyster containing tur pentine, which brought away a large number of ascarides from the rectum.
In cases of paraplegia from disease of the spinal cord, the paralysed parts are frequently troubled with cramps and startings occurring chiefly at night, and preventing sleep and occa sioning great distress to the patient. These are very often traceable to intestinal disturb ance, the presence of irritating matters, which, stimulating the mucous membrane, through its nerves excite the spinal cord, and thus produce these involuntary movements.