?2lG 



PHYSIOLOGY OF THE NERV 7 OUS SYSTEM. 



ologists to the existence of a power in the 

 nervous centres wliich 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, who 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 will 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, 

 from the seat of the primary stimulation. 



This fact was pointed out first, so far as I 

 know, by Dr. M. Hall, who regards it as 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 may 

 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 inflamma- 

 tory condition of the cord or of its membranes, 

 nor in congestion of them, but simply in a 

 state of prolonged physical 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, 

 may 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 starlings 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. 



The rigid and contracted state of the muscles 

 of paralysed limbs, which frequently 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 which 

 the nerves of the paralysed parts arise. These 

 nerves likewise participate in the irritation of 

 the cord, and thus keep the muscles 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 may 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 excitement. 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 sonic- 



