PHYSIOLOGY OF THE NERVOUS SYSTEM. 



72 1 B 



their production. And anatomists explored 

 the frequent and often intricate anastomoses 

 of nerves in their peripheral distribution with 

 the hope of finding in them some clue to the 

 explanation of these phenomena. 



To these actions I prefer to apply the name 

 physical nervous actions to mark their peculiar 

 characteristic, namely, independence of the 

 mind, and to denote that they are the result of 

 a physical change produced by a physical im- 

 pression, and therefore, in their causation, wholly 

 independent of mental influence. The term ex- 

 cito-motory has been applied to them by Dr. 

 Hall. To this term, however, there appear to 

 me to be several serious objections. First, this 

 term implies that the excitation of motion takes 

 place in no other way than by a mechanism 

 similar to that by which these movements are 

 produced. Secondly, it denotes the existence of 

 a peculiar excito-motory power different from 

 the ordinary vis nervosu, the agent in all ner- 

 vous phenomena. As if this force were not 

 capable of being roused into action at one time 

 by a mental stimulus, at another by a physical 

 stimulus, or at a third by a mental and phy- 

 sical stimulus united. Persons get into the 

 habit of using the terms "excito-motory power," 

 " excito-motory phenomena," as if this power, 

 or these phenomena were something quite pe- 

 culiar, quite sui generis, and limited to a spe- 

 cial part of the nervous system, losing sight of 

 the real truth that they differ from voluntary 

 actions only in their mode of excitation, that 

 is, by a physical and not by a mental stimulus. 

 Thirdly, it limits the reflecting power of the 

 nervous centres (i. e. the propagation of the 

 change induced by the application of a physical 

 stimulus at the periphery) to reflection from 

 sensitive to motor nerves. Now there are many 

 facts which shew that reflection may take place 

 from a sensitive to another sensitive nerve, and 

 many of the phenomena of sympathy admit of 

 no other explanation excepting on this prin- 

 ciple. And I am by no means prepared to 

 affirm that reflection may not take place from 

 motor to sensitive nerves, or even from motor 

 to other motor nerves, under circumstances of 

 an exalted polarity of the nerves and the centres. 

 Fourthly, some of these so-called e.i'cito-moton/ 

 phenomena have nothing to do with muscular 

 action. Take, for example, erection of the penis: 

 it has not been shown that muscular fibres take 

 any part in the production of this phenomenon, 

 or that the stimulus which gives rise to it does 

 more than create a change in the vessels of the 

 penis, which seems due to muscular relaxation 

 rather than to muscular contraction. The exci- 

 tation of a gland to secrete by stimulating some 

 surface connected with it, as the mammary 

 gland by stimulating the nipple, is no doubt 

 a phenomenon of the same kind, but not one 

 in which muscular fibres are excited to contract. 



The term " reflex actions," in accordance 

 with Prochaska's view of the reflecting power 

 of the nervous centre, is objectionable inas- 

 much as it fails to denote fully the physical 

 character o< the phenomena ; and, moreover, it 

 is applicable only to a class of the actions in 

 question, those, namely, in which the excitation 



VOL. in. 



of a motor or sensitive nerve takes place through 

 the primary excitation of another motor or sensi- 

 tive nerve. Either this term, however, or that 

 which I have proposed, may be used without in- 

 convenience to science because they involve no 

 particular theory, and yet sufficiently express 

 some leading feature of the phenomena, lejtec- 

 tiou at the centre, in the one case a physical 

 exciting cause of a phenomenon purely physical 

 in the other. It may be objected to the term 

 " physical nervous action " that the actions 

 produced by the mental stimulus are equally 

 physical in their intrinsic nature. When, how- 

 ever, the term is habitually used in contrast with 

 " mental nervous action," all practical difficulty 

 or objection vanishes both are physical pheno- 

 mena, but one is physical in its essence and 

 also in its exciting cause; the other is physical 

 in its essence, but mental in its cause. The 

 term physical nervous actions may be regarded 

 as a generic expression for all those nervous 

 phenomena in which the mind takes no neces- 

 sary share; reflet actions being a specific term 

 denoting those physical nervous actions of which 

 reflexion at the centre is a prominent character. 

 In this sense I shall use these terms respectively. 



By none were these phenomena more care- 

 fully studied than by Whytt and Prochaska. 

 In 1764 Whytt published his "Observations 

 on Nervous Diseases," a work full of the most 

 valuable clinical and practical information. In 

 the first chapter of this book, " on the structure, 

 use, and sympathy of the nerves," he enumerates 

 various instances of sympathetic actions, and 

 discusses the mode of their production. To 

 show that he regarded in this light the actions 

 which we are now considering, I shall quote 

 one which he adduces as an example. lie 

 says : " When the hinder toes of a frog are 

 wounded, immediately after cutting off its 

 head, there is either no motion at all excited 

 in the muscles of the legs, or a very inconsider- 

 able one. But if the toes of this animal be 

 pinched, or wounded with a penknife, ten or 

 fifteen minutes after decollation, the muscles 

 not only of the legs and thighs but also of the 

 trunk of the body are, for the most part, 

 strongly convulsed, and the frog sometimes 

 moves from one place to another.''* 



Whytt's most important work, in which this 

 subject has been most fully discussed, is the 

 essay on the vital and other involuntary morions 

 of animals, published ten years earlier, in 1754. 

 This physiologist was deeply imbued with a 

 righteous dread of materialism, which led him to 

 such extraordinary lengtlis in spiritualism, that 

 he ascribed every action and movement of the 

 body to " the immediate energy of the mind 

 or sentient principle;" while he completely 

 repudiated all notion of any mechanical dispo- 

 sition in the intimate nature of these pheno- 

 mena. As an example of his mode of reason- 

 ing upon this subject, and as further evidence 

 that he was well acquainted with the class of 

 actions which we now call reflex or phvsical, 

 the following passage from the eleventh sec- 

 tion of this essay may be cited : 



* U'hvtt's Works, 4fo. edit. p. 501. 

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