October 22. 1896J 



NA rURE 



60' 



this, \\ is clear, I say, that hetwten the molecules of the ultimate 

 fibrils branching in the Malpighian layer of the ball of the 

 finger, and the molecules within the immediate grasp of the 

 nucleus of the cell from which those fibrils start, there must be 

 ever-passing thrills — thrills, it is true, of so gentle a kind, that no 

 physical instrument we as yet possess can give us warning of 

 iheni, so gentle, that compared with them, the wave, which 

 carries what we call a nervous impulse, must appear a roaring 

 avalanche, but still thrills the token of continued movement. 

 And of such gentle impalpable unnoticed thrills, we must in the 

 future take fidl account, if we are ever to sound the real depths 

 of nervous actions. 



It is not, however, as a contribution to theoretical conceptions, 

 but rather as a method, that the results of Waller have so far 

 h.id their chief effect on the progress of physiology and medicine. 

 And I have chosen it as a thing to dwell on, because it seems to 

 ine a striking instance of the value of a method merely judged as 

 a method, and, further, because the value of its use illustrates my 

 theme that the success of any one scientific effort is contingent 

 on the converging aid of other etiurts. For some time, it is true 

 — for years, in fact — the Wallerian method was employed 

 solely or chiefly in what, without reproach, may be called the 

 smaller problems of physiology ; it settled many topographical 

 questions, it cleared our views as to the distribution of afferent 

 and etterent fibres ; it seemed to add or replace a few stones here 

 and there in the growing building, but it did not greatly change 

 the whole edifice. After a while, however, it met with two 

 helpmates — the one sooner, the other later — and, by means of 

 the three together, we have gained, and are still gaining such 

 additions to our knowledge of the ways in which the central 

 nervous system works out the acts which make up our real life, 

 as to constitute perhaps the most striking progress in the 

 physiology of our time. A wholly new chapter of nervous 

 physio|og\- has, through them, been opened up. 



The one colleague is to be found in the experiments of Fritz 

 and Hiizig ; and of Ferrier, again, e.xperiments on living 

 animals — experiments which, by demonstrating the existence of 

 definite paths for the play of nervous impulses within the central 

 nervous system, opened up paths for the play of new ideas con- 

 cerning the working of that system. I say " demonstrating the 

 existence of definite paths," for thi.s — and not the topographical 

 recognition of so many centres of hypothetical nature — is the 

 solid outcome of experiments on local stimulation of the cerebral 

 cortex. Views come and go as to what is happening when the 

 current is flitting to and fro between two electrodes placed on a 

 particular spot of the Rolandic area ; the solid ground on which 

 each view strives to establish itself is, that the particular spot is 

 joined by definite nervous paths tn particular peripheral parts. 

 I say "demonstrating the existence of particular paths," but 

 what would have been the demonstrati\'e value of the experi- 

 ments of stimulation, or of removal, by themselves, without the 

 anatomical support furnished by the Wallerian method? And 

 I may justly include within the Wallerian method, not the mere 

 tracking out the degenerated fibre by the simple means at 

 Waller's own disposal, but such finer, surer search as is afforded 

 by the later help given by the newer development of the staining 

 technique. 



They who have the widest experience of experiments on 

 living animals are the first to own that in a region of delicate 

 complexity like that of the central nervous system, the inter- 

 pretation of the results of any experimental interference may be, 

 and generally is, in the absence of aid from other sources, a 

 matter of extremest difficulty, one in which the observer, trust- 

 ing to the experiment alone, may easily lie led astray. I need 

 not labour the question what would have been the value of the 

 mere effects of stimulating or even of removal of parts of the 

 cerebral cortex, and whither would they have led us, had the 

 experimental results not been supported and their interpretation 

 guided by the teachings of the Wallerian method. It is not too 

 much to say that the experiuunts of Ferrier and his peers, 

 brilliant as they were, might have remained barren, useful only 

 as isolated bits of knowledge, or might even have led us astray, 

 had they not been complemented by anatomical facts. They 

 have not remained barren, and ihey have not led us astray. 

 The Wallerian method picked out from the tangle of nerve 

 fibres making up the white matter of the brain and spinal cord, 

 the pyramidal tract running from the Kolandic area, to the 

 origins of all the motor roots, even of the lowest, and so 

 joining hands with the experiment, made it clear that whatever 

 might be the exact nature of the events taking place in a par- 



NO . 1408, VOL. 54] 



ticular spot of the cortex of that area, that spot was, by the 

 definite paths of particular nerve fibres, put in connection with 

 definite skeletal muscles. The pyramidal tract was further 

 shown to be merely one — an important one, it is true — hut still 

 merely one of a large class. So it is that the experimental 

 results and tlie Wallerian results, not merely in that Rolandic 

 area where the results of experiment take on the grosser form 

 of readily appreciated interference with movements, but in 

 other regions where other finer, more occult manifestations of 

 nervous and psychical actions have to be dealt with are, it may 

 be slowly, but yet surely, resolving that which seemed to be a 

 hopeless tangle of interweaving and interlacing nerve fibres and 

 cells, into an orderly arrangement of which the key is seen to 

 be that each nerve filament is a path of impulses coming from 

 some spot — it may be from near, it may be from afar — where 

 events are taking place, and carrying the issue of those events 

 to some other spot, there to give rise to events having some 

 other issue. 



But a third factor was wanting to forward our insight into 

 this orderly arrangement, and especially by again affording an 

 anatomical basis to open the way towards explaining what was 

 the order of events in the spots or centres, as we call them, in 

 which the filaments began or ended, and what w as the mechanism 

 of the change of events. This, I venture to think, we may find 

 in the special histological method which, however much its use- 

 fulness, has been enhanced by its subsequent development in the 

 hands of Cayal, Kolliker, and others, as well as by the coincident 

 methyl-blue method we owe to Golgi. The final word has not 

 yet been said as to the exact meaning and value of the black 

 silver |iictures which that method places Ijefore us ; but this, at 

 least, may be asserted that by means of them the progress of our 

 knowledge of the histological constitution of the central neivous 

 system has within the last few years made strides of a most 

 remarkable kind. It may be that those pictures are in some of 

 their features misleading, it may be that the terminal arborisa- 

 tion, and their lack of continuity with the material of the 

 structures which they grasp, does not afford an adequate 

 explanation of the change in the nature of the nervous impulses 

 which takes place at the relays of which the arborisations seem 

 the token ; it may be, indeed it is probable, that we have yet 

 much to learn on these points. But notwithstanding this, it must 

 still be said that, by the help of this method, our know ledge of 

 how the fibres run, where they begin and where they end within 

 the brain and spinal cord, has advanced, and is advancing in a 

 manner which, to one who looks back to the days when Huxley 

 was studying within these walls, seems little short of marvellous. 



Let me once more repeat, the value of this silver method is 

 not an intrinsic one, it has its worth because it fits in with other 

 methods, it is available on account of what is known apart from 

 it. I imagine that if in 1842 Huxley, at Wharton Jones' sug- 

 gestion, had invented the silver method, it would have remained 

 unknown and unused. The time for it had not then come. The 

 full fruition which it has borne, and is bearing in our day has 

 come to it, because it works hand in hand with the two other 

 methods, of which I have spoken— the Wallerian and the 

 experimental method. 



It is these three working together which have brought forth 

 what I may venture to call the wonders which we have seen in 

 our days, and I cannot but think that what we have seen is but 

 an earnest of that which is to come. In no branch of physiology 

 is the outlook more promising, even in the immediate future, 

 than in that of the central nervous system. But surely I do it 

 wrong to call it merely a branch of physiology. It is true that 

 if we judge it by even the advanced knowledge of to-day, it takes 

 up but a small part of the whole teaching of the science ; 

 but when we come to know about it that which we are to know, 

 all the re.st of physiology will shrink into a mere appendage of 

 it, and the teacher of the future will hurry over all that to which 

 to-day we devote so much of the year's course, in order that he 

 may enter into the real and dominant part. 



There is no need for me to expound in detail how the know- 

 ledge gained by the three methods, of which I have been 

 sjieaking, in laying bare the secrets of nervous diseases, and 

 opening up the way for successful treatment accurate and trust- 

 worthy prognosis, has helped onward the art of medicine. Even 

 the younger among us must be impressed when he compares 

 what we know to-day of the diseases of the nervous system 

 with what we know, I will not say fifty, but even twenty, nay 

 even ten, years ago. Do not for a moment suppose that I am 

 attempting to maintain that the great clinical progress which 



