442 



NATURE 



[Sept. 8, 1881 



investigator. In tlie face of liistorical fact it is impossible to 

 regard him as the discoverer of tlie " reflex function of tiie 

 spinal cord," but we do not the less owe him gratitude for the 

 application he made of the knowledge he had gained by experi- 

 ments on animals to the study of disease. For no one who is 

 acquainted with tlie development of tlie branch of practical 

 medicine which relates to the diseases of the central nervous 

 system will hesitate in attributing the rapid progress which has 

 been made in the diagnosis and treatment of these diseases, to 

 the impulse given by Dr. Marshall Hall to the study of nervous 

 pathology. 



In the nund of Dr. Marshall Hall the word reflex had a very 

 restricted meaning. The term "excito-motary function," which 

 he also used, stood in his mind for a group of phenomena of 

 which it was the sole characteristic that a sensory impression 

 produced a motor response. During the thirty years which liave 

 elapsed since his death, the development of meaning of the word 

 reflex has been comparable to that of a plant from a seed. The 

 original conception of reflex action has undergone, not only ex- 

 pansion, but also modification, so that in its wider sense it may 

 be regarded as the empirical development of the philosophical 

 views of the animal mechanism promulgated by Descartes. Not 

 that the work of the past thirty years I.iy which the physitJogy of 

 the nervous system has Ijeen constituted can be attributed for a 

 moment to the direct influence of De-cartes. The real epoch- 

 maker here was Johannes Midler. There can be no doubt that 

 Descartes' physiological speculations were well known to him, 

 and that his large acquaintance with the thought and work of his 

 predecessors conduced, with his own powers of observati.in, to 

 make him the great man that he was ; but to imagine that his 

 ideas if the mechanism of the nervous system were inspired, or 

 the investigations by which, contemporaneously with Dr. Mar- 

 shall Hall, he demonstrated the fundamental facts of reflex 

 action, were l■ugge^ted by the animal automatism of Descartes, 

 seems to me wholly improbalde. 



I propose, liy way of conclu-ion, to attempt to illustrate the 

 nature of reflex action in the lai-ger sense, or, as I should prefer 

 to call it, the Automatic Action of Centtes, by a single example 

 — that of the nervous mechanism by which the circulation is 

 regulated. 



The same year that J. R. Mayer published his memorable 

 essay, it was discovered by E. H. Weber that, in the vagus 

 nerve, which springs from the medulla oblongata and proceeds 

 therefrom to the heart, there exist channels of influence by 

 which the medulla acts on that wonderful muscular mechanism. 

 Almost at the same time with this, a series of discoveries ' were 

 made relating to the circulation, which, taken together, must be 

 regarded as of equal importance n\ ith the original discovery of 

 Harvey. First, it was found. by Henle that the arterial blood- 

 vessels by which blood is distributed to brain, nerve, muscle, 

 gland, and other organs, are provided w ith muscular walls like 

 those of the heart itself, by the contraction or ddatation of ^^hich 

 the : upply is increased or diminished according to the require- 

 ments of the particular organ. Secondly, it was discovered 

 simultaneously, but independently, by Bro»n-Sequard and 

 Augustus Waller, that these arteries are connected by nervous 

 channels of influence with the brain and spinal cord, just as the 

 heart is. Thirdly, it was demonstrated by Bernard that «hat 

 may be called the heart-managing channels spring from a small 

 spot of grey substance in the medulla oblongata, which we now 

 call the "heart-centre"; and a little later by Schiif, that the 

 artery-regulating channels spring from a similar head-central 

 office, also situated in the medulla oblongata, but higher up, and 

 from subordinate centres in the spinal cord. 



If I had the whole day at my disposal and your patience were 

 inexhaustible, I might attempt to give an outline of the is'ues 

 to which these five di coveries have led. As it is, I must limit 

 myself to a brief discus ion of their relations to each other, in 

 order that we may learn something from them as to the nature 

 of automatic action. 



Sir Isaac Newton, whi^, although he knew nothing about the 

 structure of nerves, made some shrewd forecasts about their 

 action, attributed to those which are connected with muscles an 



' The dates of the discoveries relating to this subject here referred to are 

 as fullous:— Muscular Struclure of Arteries, Henle. 1841 ; Function uf 

 Cardiac Vagus, E. H. Weber, 1845 : C. nstricting Nerves of Arteries, B. 

 S^quaid, 1852, Aug. Waller, 1853; Cardiac Centre, Bernard. 18 = 8; Vascu- 

 lar Centre, Schiff, 1858; Dilating Nerves, Schiff, 1854: Eckhard, 1S64: 

 Love'n, 1866. Of the m.re recent researches by which the further elucida- 

 tion of the mechanism by which the distribution ff blocd is adapted to the 

 requirements of each organ, the n.ost impi.rtant are those of Ludwig and 

 his pupils and of Heidenhain. 



alternative function. He thought that by means ( f motor nerves 

 the brain could determine either relaxation or contraction of 

 muscles. Now as regards ordinary muscles, we know that this 

 is not the case. We can will only the shortening of a muscle, 

 not its lengthening. When Brown- Sequard discovered the 

 function of the motor nerves of the blood-vessels, he assumed 

 that the same limitation was applicable to it as to that of mus- 

 culai- nerves in general. It was toon found, liowever, that this 

 assun;ption was not true in all cases — that there were certain 

 instances in which, when the vascular nerves were interfered w ith, 

 dilatation of the blood-vessels, consequent on relaxation of their 

 muscles, took place ; and that, in fact, the nervous mechanism 

 by which the circulation is regulated is a highly-complicated one, 

 of which the best that we can say is that it is perfectly adapted 

 to its purpose. For while every organ is supplied h ith muscular 

 arteries, and every artery with vascular nerves, the influence 

 ■^^•hich these transmit is here relaxing, there constricting, accord- 

 ing (i) to the function which the organ is called upon to dis- 

 charge ; and (2) the degree of its activity at the time. At the 

 same time the whole mechanism is controlled by one and the 

 same central office, the locality of « hich we can determine with 

 exactitude by experiment on the living animal, notwithstanding 

 that its structure afl'ords no indication whatever of its fitness for 

 the function it is destined to fulhl. To judge of the complicated 

 nature of this function we need only consider that in no single 

 organ of the body is the supply of blood required always the 

 same. The brain is during one hour hard at work, dm-ing 

 the next hour asleep ; the muscles are at one moment in severe 

 exercise, the next in complete repose ; the liver, which before a 

 meal is inactive, during the process of digestion is turgid with 

 blood, and bu ily engaged in the chemical work which belongs 

 to it. For all these vicissitudes the ti'act of grey substance v hich 

 we call the I'ascular centre has to provide. Like a skilful 

 steward of the animal household, it has, so to speak, to exercise 

 perfect and unfailing foresight, in order that the nutritive mate- 

 rial which serves as the oil of life for the maintenance of each 

 vital process, may not be w anting. The fact that this wonderful 

 function is localised in a particular bit of grey substance is what 

 is meant by the expression " automatic action of a centre." 



But up to this point we have looked at the subject from one 

 side only. 



No state ever existed of w hich the administration was exclu- 

 sively executive — no government which was, if I may be excused 

 the expression, absolutely absolute. If in the animal organism 

 we impose on a centre the responsibility of governing a particu- 

 lar mechanism or process, independently of direction from above, 

 we must give that centre the means of being itself influenced by 

 what is going on in all parts of its area of government. In 

 other words, it is as essential that there should be channels of in- 

 formation passing inwards, as that there should be channels of 

 influence passing outwards. Now what is the nature of these 

 channels of information ? Experiment has taught us not merely 

 with reference to the regulation of the circulation, but with re- 

 ference to all other automatic mechanisms, that they are as 

 various in their adaptation as the outgoing channels of influence. 

 Thus the vascular centre in the medulla oblongata is so cognisant 

 of the chemical condition of the blood which flows through it, 

 that if too much carbonic acid gas is contained in it, the centre 

 acts on information of the fact, so as to increase the velocity of 

 the blood-stream, and so promote the arterialisation of the 

 blood. Still m re strikingly is this adaptation seen in the 

 arrangement by which the balance of pressure and resistance in 

 the blood-vessels is regulated. The heart, that wonderful 

 muscular machine by which the circulation is maintained, is con- 

 nected with the centre, as if by two telegraph wires — one of 

 which is a channel of influence, the other of information. By 

 the latter the engineer who has charge of that machine seiids 

 information to headquarters whenever the strain on his machine 

 is excessive, the certain respon^ e to w hich is relaxation of the 

 arteries and diminution of pressui-e. By the former he is enabled 

 to adapt its rate of working to the work it has lo do. 



If Dr. Whytt, instead of cutting off the he.id of his fi-og, had 

 removed only i's brain — i.e., the organ of thought and conscious- 

 ness — he would have been more astonished than he .ictually was 

 at the result ; for a frog so conditioned exhibits, as regarc's its 

 bodily movements, as perfect adaptiveness as a nonnal frog. 

 But vei7 little careful observation is sufficient to show the differ- 

 ence. Being incapable of the simplest ment 1 acts, this true 

 animal automaton has no notion of requiring food or of seeking 

 it, has no motive for moving from the place it happens to 



