718 



CONTRACTILITY. 



on the surface, closing the eyelids when the 

 eyes are offended by bright light, swallowing, 

 breathing, coughing, sneezing, vomiting, ex- 

 pulsion of faeces and urine, &c. consequent 

 on certain sensations of the fauces, lungs, air- 

 passages, nostrils, stomach, rectum, or blad- 

 der. Such muscular actions, excited by irri- 

 tation of distant parts, have been generally but 

 vaguely described as the effects of Sympathies 

 of one part of the living body with another. 

 It is well ascertained that they are effected 

 through the motor nerves (or certain of the 

 motor nerves) of the muscles concerned in 

 them ; and their dependence on the Sensations, 

 and therefore on the sensitive nerves, of the 

 parts from the irritation of which they originate, 

 has been sufficiently illustrated by Haller, 

 Whytt, Monro, and others.* 



It has also been observed, by Haller and 

 Whytt, but more frequently and carefully by 

 Legallois,f Flourens, and Mayo,J that in 

 many animals, (most remarkably in cold- 

 blooded, or young warm-blooded animals,) 

 even after the removal of the brain, as long 

 as the circulation can be maintained, move- 

 ments of the kind now in question go on, 

 or may be excited by irritation of the sur- 

 faces; and that if the spinal cord be divided 

 into several parts by transverse sections, such 

 movements may still be excited in the muscles 

 supplied from each part, by irritation of the 

 portion of the skin which has its nerves from 

 that part of the cord. These facts have (as is 

 believed) usually been thought to denote, that a 

 certain degree of Sensation remains under these 

 circumstances, in connection with the living 

 state of the spinal cord, or of portions of the 

 spinal cord, and medulla oblongata, indepen- 

 dent of the brain ; and that it is still through 

 the intervention" of sensation, that irritation 

 of the surface of the body excites any con- 

 traction of muscles. Dr. Marshall Hall has 

 lately described phenomena precisely of this 

 description, under the title of Excito-motory 

 phenomena, and as proofs of what he terms 

 the Reflex Function of the Spinal Chord 

 a power of exciting contraction in mus- 

 cular fibres connected with it, which he 

 supposes that organ to possess, equally inde- 

 pendently of sensation as of volition ;|| and as 

 it seems hardly possible to be quite certain of 

 the existence of Sensation in the case of the 

 mutilated animal, this language is perhaps 

 philosophically correct ; but the probability of 

 the existence of Sensation in such circum- 

 stances must be allowed to be very great ; and 

 at all events, that sensation is an essential part of 



* It is obvious that such motions, excited di- 

 rectly by sensations, cannot be accurately distin- 

 guished from those voluntary actions which are 

 called Instinctive, as being prompted by the in- 

 stincts, distinct from strictly intellectual acts, 

 which are linked by nature with the sensations of 

 certain parts of the body. 



t Experiences sur le Principe de la Vie, 



$ Outlines of Physiology, second edit. p. 282 

 and Anat. and Physiol. Comms. 



Phil. Trans. 1833, p. 635. 



I] See particularly p. 640. 



the connection between the irritation of distant 

 parts, and the excitement of involuntary mus- 

 cular contractions of voluntary muscles, for 

 useful purposes, in the entire and healthy 

 body, may be held to be a point well esta- 

 blished by the observations of Haller, Whytt, 

 Monro, and others, on such sympathetic actions. 

 Accordingly, those actions, in the entire body, 

 which Dr. M. Hall ascribes to the reflex func- 

 tion,* are the same, or similar to those, which 

 have been fully treated by Dr. Whytt and others 

 as sympathetic actions, or actions of voluntary 

 muscles excited by sensations. 



But Dr. Hall has fixed the attention of phy- 

 siologists on this class of facts, and has illus- 

 trated by experiments their independence of 

 the Brain, and dependence on the Spinal Cord 

 exclusively, and in this conclusion he is sup- 

 ported by many facts previously recorded by 

 Le Gallois, Magendie, Flourens, and others. 



It is further to be observed, that the contrac- 

 tions of voluntary muscles, which are supplied 

 by the nerves of the Symmetrical class of Sir 

 C. Bell, while they are excited through the one 

 set of filaments comprising those nerves, are 

 made known to our consciousness by the others 

 or sensitive filaments, and constitute the im- 

 portant class of Muscular Sensations. Of the 

 movements of the strictly involuntary muscles, 

 the heart, stomach, and bowels, and even the 

 bladder, (supplied by irregular nerves,) we 

 have, in the perfectly healthy state, no intima- 

 tion, although they frequently become percepti- 

 ble to us in disease, or when over-excited. But 

 contractions of some of these involuntary mus- 

 cles also are pretty certainly excited by certain 

 Sensations, as, e. g. a certain degree of antipe- 

 ristaltic movement in the stomach by the feel- 

 ing of nausea, and a certain movement of the 

 pharynx and oesophagus by the sensations in 

 the fauces, which prompt the act of deglutition ; 

 and in such cases, although not attended with 

 consciousness, they are in all probability excited 

 through the nerves of these muscular parts. 

 Accordingly, the pharynx and oesophagus have 

 been observed by Mr. Mayo, and the stomach 

 by Breschet, Milne Edwards, and others, to 

 be exceptions to the general rule of involuntary 

 muscles being inexcitable by irritation of their 

 nerves. 



The old distinction of muscles into Volun- 

 tary, Involuntary, and Mixed, is very deficient 

 in precision, so far as the last class is concerned. 

 The true distinction is, of muscular contrac- 

 tions, into those excited in the natural state by 

 Mental Stimuli, and through the intervention 

 of Nerves (qui soli in corpore mentis sunt mi- 

 nistri) and those excited by Physical Stimuli, 

 acting on the muscles themselves, whereas the 

 intervention of nerves is a theory, not an esta- 

 blished fact. The first class admits obviously, 

 from what has been stated, of a division into 

 movements excited by the Will, which depend 

 on the Brain, and movements excited by invo- 

 luntary mental acts, especially by Sensations, 

 which depend only on the Spinal Cord and 

 medulla oblongata. The Will acts only on 



* P. 653 et seq. 



