04 



NATURE 



\M. 



ov. 30, 1876 



" the sensations accompanying muscular action being re- 

 peated as often as the muscular action itself, the organic 

 nexus between the motor and tactile centres becomes so 

 welded, that this sensori-motor cohesion enters like a 

 compound chemical radical as a simple factor into every 

 association which motor centres can form with other 

 motor centres and with sensory centres in general " (p. 

 268) ; then surely this, while it satisfactorily accounts for 

 the motions following excitation of sensory regions, leaves 

 unexplained the facts of other such excitations not being 

 followed by motions (comp. p. 231), and raises the question 

 whether all motions are not due to sensory excitation ? 

 On the first point let us ask why the optic thalami — said 

 by him to be sensory centres— do not respond by motor 

 manifestations when stimulated ? He regards this " as 

 sufficient of itself to dispose at once of the views of those 

 who would attribute motor functions to these ganglia. 

 The fact that lesions of the optic thalami cause paralysis 

 of motion proves nothing regarding the real functional 

 significance of these ganglia " (p. 239). Agreed ; but then 

 why does he not equally conclude that absence of paralysis 

 of motion, when the corpora striata are destroyed, dis- 

 proves the motor function he assigns to these ganglia, 

 especially since direct stimulation of these ganglia does 

 not produce motions ? 



Then, again, if sensorial excitations produce move- 

 ments by playing upon the motor centres, why not adopt 

 the view which regards all cerebral excitation as sen- 

 sorial ? The hypothesis of motor centres in the cortex 

 would thus be resolved into the fact that particular sen- 

 sations excite particular movements ; and the localisation 

 of spots on the cortex would be no more than analogous 

 localisations on the skin — the sensation excited by tickling 

 the sole of the foot, causing different movements from those 

 caused by the same stimulus applied to the heel or instep. 



Dr. Ferrier has explicitly declared that " there is no 

 reason to suppose that one part of the brain is excitable 

 and another not. The question is how the stimulation 

 manifests itself" (p. 130). This is in accordance with what 

 I have maintained, namely, that neural processes are 

 uniform in character, the diversity of their results — sen- 

 sation, motion, or secretion — depending on anatomical 

 connections. In itself, a neural process is no more a 

 sensation than it is a secretion. To determine a motor 

 centre, therefore, we must look beyond the cortex, and 

 detect its anatomical relations to the motor-apparatus. 

 Do Dr. Ferrier's experiments prove that the area of the 

 cortex, assigned by him as the motor area, has such ana- 

 tomical relations to the motor apparatus, and the sen- 

 sorial area such relations to the sensory organs, that we 

 can speak of their activities as motor and sensorial 

 functions ? In other words, are the cortical areas to be 

 regarded as playing the part of central functions or only of 

 peripheral incitations ? 



He has argued his view with such force of fact and 

 suggestion that I have little doubt of his carrying most 

 readers with him ; and because I dissent from his view 

 I must occupy all my remaining space by endeavouring to 

 weaken the effect of his argumentation. He considers that 

 the indications naturally suggested by the observed facts 

 of electrical stimulation are proved by the observed effects 

 of disease and extirpation. Stimulation of particular 

 spots is followed by definite movements ; destruction of 



those spots is followed by paralysis of those movements. 

 The reader is led captive by what seems irresistible logic- 

 The evidence seems decisive. How if the evidence 

 should be illusory ? That it is illusory may be shown, I 

 think, under three heads : — 



First Head. — The Italian physiologists Lussana and Le- 

 moigne have specially called the attention of experimenters 

 to the fact that very many recorded contradictions result 

 from the not distinguishing between the first and second 

 experimental periods, namely, the effects observable soon 

 after the operation, and the effects which are observable 

 when the disturbance has settled down, and the organism 

 has recovered something like vs normal state (" Fisiologia 

 dei Centri Nervosi," 1871). The first period comprises 

 what may be called the effects of Disturbance of Function; 

 the second period the effects of Removal of Function. The 

 distinction, so fruitfully introduced by Dr. Hughlings 

 Jackson, of discharging lesions and destroying lesions 

 falls under the same conception. I will only add that 

 neither the effects of Disturbance nor the effects of Re- 

 moval are to be taken as conclusive evidence that the 

 function disturbed or removed is the function of the 

 organ operated on ; but that whenever a function per- 

 sists, or reappears, after the destruction of an organ, this 

 is absolutely conclusive against its being the function of 

 that organ. 



This premised, I must suggest that Dr Ferrier's experi- 

 ments cannot be considered as conclusive, because he 

 was unable to keep the animals alive long enough to allow 

 the effects of Disturbance to subside, so as to leave only 

 the effects of Removal to be estimated. And this is the 

 more to be emphasised because in some instances the 

 animals did survive long enough to show some subsidence 

 of the disturbance and some reappearance of the lost 

 functions. Now the reappearance of a function after the 

 destruction of an organ admits of but two interpretations 

 — either the function was arrested as an effect of the dis- 

 turbance, or its organ was destroyed, and another organ 

 had vicariously taken its place. This second interpreta- 

 tion is much in vogue, and has received the name of the 

 law of Substitution. The notion that a function can be 

 driven from organ to organ, " like a sparrow driven from 

 one branch to another," as Goltz picturesquely says, is 

 surely raising Hypothesis to the «th power? Dr. Ferrier 

 without adopting the first of the two interpretations, 

 argues against the second with his usual force ; replacing 

 it by one which is physiologically more consistent, namely, 

 that " there is no direct estabhshment of new centres in 

 place of those which have been lost, but that those which 

 remain may indirectly without assuming new function^ 

 make up for the loss, to some extent at least." In these 

 cases " the path from impression to action is not as in thd 

 ordinary course of volition through the cortical motoJ 

 centres to the corpus striatum, and thence downwards t<^ 

 the motor nuclei and motor nerves, but through the basa 

 ganglia directly." This fails to meet the case when, foij 

 example, the function of .vision on one side disappear 

 after removal of its assigned cortical centre, and never-^ 

 theless reappears. We cannot get the ear to do the work 

 of the eye ; and if touch does indirectly make up for loss 

 of sight, it is by a slow process of acquisition ; whereas 

 the animal recovers its lost sight, and that in the course 

 of a few days. 



