NATURE 



[September 8, 1904 



THE BRITISH ASSOCIATION. 

 SECTION I. 



PllVSIOLOGV. 



Opening Address by Prof. C. S. Sherrington, M.A., 

 D.Sc, M.D., LL.D., F.R.S., President of the Section. 



Correlation of Reflexes and tlie Principle of the Common 



Path. 

 It has been lightly said that this Association meets to 

 cultivate less muses than amusements. The two are 

 compatible, and here happily the muses not merely 

 nine, but ten ; for we surely include among the muses 

 " Physiologia." Here in Cambridge our muse admits 

 frankly that a mistake has been made about Parnassus — 

 it is not a mountain but a fiat place, almost fenny, once 

 worried by mosquitoes, and now immune from all worries. 



Perhaps the confusion between Parnassus and a mountain 

 was due to the Gog-Magog hills. Those hills our muse 

 has haunted and still haunts. She has votaries there ; 

 among them one who instituted her worship in this place, 

 a teacher whose powerful appeal attracted disciples from all 

 sides, one whose enthusiasm was, moreover, never narrowed 

 to a single science alone, but floods all biology. With 

 Cambridge and Physiology the name of Sir Michael Foster 

 rises to the lips as an indissoluble sequence. So it will ever 

 be; and it must give him pleasure, as it gives us, to have 

 for his successor here one of his first pupils, one associated 

 far and wide with that which Physiology treasures as 

 always golden, the discovery of imperishable facts. 



When this Section last met, two years ago, its President, 

 Prof. Halliburton, reviewed for us the existing position of 

 chemical physiology. We cannot from the nervous system 

 draw themes of such general attractiveness as the new^ 

 biochemistry, with its startling reactions, its varied hypo- 

 theses, its toxophores, haptophores, amboceptors, and other 

 fairy-like agents. 



Physiology studies the nervous system from three main 

 points of view. One of these regards its processes of nutri- 

 tion. Nerve-cells, as all cells, lead individual lives, breathe, 

 dispense their own stores of energy, repair their own sub- 

 stantial waste, are, in short, living units, each with a 

 nutrition more or less centred in itself. The problems of 

 nutrition of the nerve-cell and of the nervous system, though 

 partly special to this specially differentiated form of cell life, 

 are, on the whole, accessible to the same methods as is 

 nutrition in other cells and in the body as a whole. 



But beside the essential functions common to all living 

 cells, the cells of the nervous system present certain which 

 are specialised. Among properties of living matter, one by 

 Its high development in the nerve-cell mav be said to 

 characterise it. I mean the cell's transmission of excite- 

 ment spatially along itself and thence to other cells. This 



conductivity " is the specific physiological property of 

 nerve-cells wherever they exist. Its intimate nature is, 

 therefore, a problem coextensive with the existence of nerve- 

 cells, and enters as a factor into every question concerning 

 the specific reactions of the nervous system. 



Thirdly, physiology seeks in the nervous system how by 

 Its conductivity " the separate units of an animal body 

 are welded into a single whole, and from a mere collection 

 of organs there is constructed an individual animal. 



This third line of inquiry, though greatly needing more 

 data from the second and the first, must in the meantime 

 go forward of itself. It is at present busied with many 

 questions that seem special— hence its work is generally 

 catalogued as Special Physiology. But it includes general 

 problems. In the time before us I would venture to put 

 before you one of these. 



When we regard the nervous system as to this, which I 

 w^ould term its integrative function, we can distinguish two 

 main types of system according to the mode of union of the 

 conductors— (i.) the nerve-net system, such as met in 

 Medusa and in the walls of viscera, and (ii.) the synaptic 

 systern, such as the cerebro-spinal system of Arthropods 

 and \ ertebrates. In the integrative function of the nervous 

 system the unit mechanism is the reflex. The chain of 

 conduction in the reflex is a nervous arc, running from a 

 receptor organ to an effector organ, e.g. from a sense-organ 

 to a limb-muscle. We may still, 1 think, conveniently 



accept the morphological units termed neurones as units of 

 construction of the reflex arc. It may be that these neurones 

 are in some cases not unicellular but pluricellular. That 

 question need not detain us now. Accepting the neurone 

 as the unit of structure of the reflex chain, the characteristic 

 of the synaptic system is that the chain consists of neurones 

 jointed together in such a way that conduction along the 

 chain seems possible in one direction only. These junctions 

 of the neurones are conveniently termed synapses. The 

 irreversible direction of the conductivity along the neurone 

 chain is probably referable to its synapses. This 

 irreciprocity of conduction especially distinguishes the 

 synaptic nervous system from the nerve-net system. 



The first link of each reflex chain is a neurone which starts 

 in a receptor organ, e.g. a sense-organ. A receptive field, 

 e.g. an area of skin, is always analysable into receptive 

 points, and the initial nerve-path in every refle.x arc starts 

 from a receptive point or points. A single receptive point 

 may play refiexly upon quite a number of different effector 

 organs. It may be connected through its reflex path with 

 many muscles and glands in various parts. Yet all its 

 reflex arcs spring from the one single shank, so to say ; 

 that is, from the one afferent neurone that conducts from 

 the receptive point at the periphery into the central nervous 

 organ. 7"his neurone dips at its deep end into the great 

 central nervous organ, the cord or brain. There it enters 

 a vast network of conductive paths. In this network it 

 forms manifold connections. So numerous are its potential 

 connections there, that, as show-n by the general convulsions 

 induced under strychnia-poisoning, its impulses can dis- 

 charge practically every muscle and effector organ in the 

 body. Yet in normal circumstances the impulses conducted 

 by it to this central network do not irradiate there in all 

 directions. Though their spread over the conducting net- 

 work does, as judged by the effects, increase with increase 

 of stimulation of the entrant path, the irradiation remains 

 limited to certain lines. Under weak stimulation of the 

 entrant path these lines are sparse. The conductive net- 

 work affords, therefore, to any given path entering it some 

 communications that are easier than others. This canal- 

 isation of the network in certain directions from each 

 entrant point is sometimes expressed, borrowing electrical 

 terminology, by saying that the conductive network from 

 any given point offers less resistance along certain circuits 

 than along others. This recognises the fact that the con- 

 ducting paths in the great central organ are arranged in 

 a particular pattern. The pattern of arrangement of the 

 conductive network of the central organ reveals somewhat 

 of the integrative function of the nervous system. It tells 

 us what organs work together in time. The impulses are 

 led to this and that effector organ, gland or muscle, in 

 accordance with the pattern. The success achieved in the 

 unravelling of the conductive patterns of the brain and cord 

 is shown by the diagrams furnished by the works of such 

 investigators as Edinger, E-xner, Flechsig, van Gehuchten, 

 v. Lenhossek, v. Monakow, Ramon, and Schafer. Know- 

 ledge of this kind stands high among the neurological 

 advances of our time. 



But we must not be blind to its limitations. The achieve- 

 ment may, though more difficult, be likened to tracing the 

 distribution of blood-vessels after Harvey's discovery gave 

 them meaning, but before the vasomotor mechanism was 

 discovered. The blood-vessels of an organ may be turgid 

 at one time, constricted almost to obliteration at another. 

 With the conductive network of the nervous system the 

 temporal changes are even greater, for they extend to 

 absolute withdrawal of nervous influence. Our schemata 

 of the pattern of the great central organ take no account of 

 temporal data. But the pattern of the web of conductors 

 is not really immutable. Functionally its details change 

 from moment to moment. In any active part it is a web 

 that shifts from one pattern to another, from a first to a 

 second, from a second to a third, then back perhaps to the 

 first, and then to a fourth, and so on backwards and for- 

 wards. As a tap to a kaleidoscope, so a new stimulus that 

 strikes the central organ causes it to assume a partially 

 new pattern. The pattern in general remains, but locally 

 the patterns are in constant flux of back and forward change. 

 These time-changes offer, I venture to think, a study 

 important for understanding the integrative function of the 

 nervous system. 



NO. 1819, VOL. 70] 



