SCIENCE. 



5ii 



years after that Whytt and Hales made the fundamental 

 experiments on beheaded frogs, by which they showed 

 that the involuntary motions which such preparations 

 execute cease when the whole of the spinal cord is de- 

 stroyed — that if the back part of the cord is destroyed, 

 the motions of the hind limbs, if the fore part, those of 

 the fore limbs cease. It was in 1751 that Dr. Whytt pub- 

 lished in Edinburgh his work on the involuntary motions 

 of animals. After this the next great step was made 

 within the recollection of living physiologists : a period 

 to which, as it coincided with the event which we are now 

 commemorating — the origin of the British Association — 

 I will now ask your special attention. 



Exactly forty-nine years ago, Dr. Marshall Hall com- 

 municated to the Zoological Society of London, the 

 first account of his experiments on the reflux function of 

 the spinal cord. The facts which he had observed, and 

 the conclusions he drew from them, were entirely new to 

 him, and entirely new to physiologists to whom his com- 

 munication was addressed. Nor can there be any reason 

 why the anticipation of his fundamental discovery by Dr. 

 Whytt should be held to diminish his merit as an original 

 investigator. In the face of this historical fact it is im- 

 possible to regard him as the discoverer of the " reflex- 

 function of the spinal cord," but we do not the less owe 

 him gratitude for the application he made of the knowl- 

 edge he had gained by experiments on animals to the study 

 of disease. For no one who is acquainted with the de- 

 velopment of the branch of practical medicine which re- 

 lates to the disease 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 mind 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 character- 

 istic that a sensory impression produced a motor re- 

 sponse. During the thirty years which have 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 un- 

 dergone, not only expansion, but also modification, so 

 that in its wider sense it may be regarded as the empiri- 

 cal development of the philosophical views of the animal 

 mechanism promulgated by Descartes. Not that the 

 work of the past thirty years by which the physiology of 

 the nervous system has been constituted can be attrib- 

 uted for a moment to the direct influence of Descartes. 

 The real epoch-maker here was Johannes Muller. There 

 can be no doubt that Descartes' physiological specula- 

 tions were well known to him, and that his large ac- 

 quaintance with the thought and work of his predeces- 

 sors conduced, with his own powers of observation, to 

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

 that his ideas of mechanism of the nervous system were 

 inspired, or the investigations by which, contempora- 

 neously with Dr. Marshall Hall, he demonstrated the 

 fundamental facts of reflex action, were suggested by the 

 animal automatism of Descartes, seems to me wholly 

 improbable. 



I propose, by way of conclusion, to attempt to illus- 

 trate the nature of reflex action in the larger sense, or, 

 as I should prefer so call it, the Automatic Action of 

 Centres, by a single example — that of the nervous me- 

 chanism by which the circulation is regulated. 



although it was placed under the supervision of the " Ame raisanable " 

 which had its office in the pineal gland, was capable of working independ- 

 ently. As instances of i his mechanism Descartes gives the withdrawal of 

 the foot on the approach of hot objects, the actions of swallowing, yawn- 

 ing, coughing, etc. As it is necessary that, in the performance of these 

 complicated motions, the muscles concerned should contract in succes- 

 sion, provision is made for this in the construction of the system of tubes, 

 which represent the motor nerves. The weakness of the scheme lies in 

 the absence of fact basis. Neither threads nor pores nor tubes have any 

 existence. 



The same year that J. R. Mayer published his mem- 

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

 in the vagus nerve, which springs from the medulla ob- 

 longata and proceeds therefrom to the heart, there exists 

 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 with the original discov- 

 ery 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 pro- 

 vided with muscular walls like those of the heart itself, 

 by the contraction or dilation of which the supply is in- 

 creased or diminished according to the requirements of 

 the particular organ. Secondly, it was discovered simul- 

 taneously, but independently, by Brown-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 what may be called the heart-managing 

 channels spring from a small spot of gray substance in 

 the medulla oblongata, which we now call the " heart-cen- 

 tre ;" and a little later by Schiff, that the artery-regula- 

 ting 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 pa- 

 tience were inexhaustible, I might attempt to give 

 an outline of the issues to which these five discoveries 

 have led. As it is, I must limit myself to a brief dis- 

 cussion 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, who, 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 alternative function. He thought that by 

 means of 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 length- 

 ening. 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 

 muscular nerves in general. It was soon found, how- 

 ever, that this assumption was not true in all cases — that 

 there were certain instances in which, when the vascuk.r 

 nerves were interfered with, dilatation of the blood-ves- 

 sels, 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 

 with muscular arteries, and every artery with vascular 

 nerves, the influence which these transmit is here relax- 

 ing, there constricting, according (1) to the function 

 which the organ is called upon to discharge ; and (2) the 

 degree of its activity at the time. At the same time the 

 whole mechanism is controlled by one and the same cen- 

 tral office, the locality of which we can determine with 

 exactitude by experiment on the living animal, notwith- 

 standing that its structure affords no indication what- 

 ever of its fitness for the function it is destined to fulfill. 

 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, during the next hour 



1 The dates of the discoveries relating to this subject here referred to 

 are as follows: — Muscular Structure of Arteries, Henle, 1841 ; Function of 

 Cardaic Vagus, E. H. Weber, 1845; Constricting Nerves of Arteries, H. 

 Sequard, 1858 ; Aug. Waller, 1853 ; Cardiac Centre, Bernard, 1858 ; Vas- 

 cular Centre, Schiff, 1858 ; Dilating Nerves, Schiff, 1854 ; Eckhard, 1864 ; 

 Loven, i860. Of the more recent researches by which the further eluci- 

 dation of the mechanism by which the distribution of blood is adapted to 

 the requirements of each organ, the most important are those of Ludwig 

 and his pupils and of Heidenhain. 



