tion, for control of the sphincters, etc., which could be excited to activity by tactile stimuli and as readily reinhibited by others simultaneously applied.* We may therefore plausibly suppose that the rapid reappearance of motility, vision, etc., after their first disappearance in consequence of a cortical mutilation, is due to the passing off of inhibitions exerted by the irritated surface of the wound. The only question is whether all restorations of function must be explained in this one simple way, or whether some part of them may not be owing to the formation of entirely new paths in the remaining centres, by which they become 'educated' to duties which they did not originally possess. In favor of an indefinite extension of the inhibition theory facts may be cited such as the following: In dogs whose disturbances due to cortical lesion have disappeared, they may in consequence of some inner or outer accident reappear in all their intensity for 24 hours or so and then disappear again. † In a dog made half blind by an operation, and then shut up in the dark, vision comes back just as quickly as in other similar dogs whose sight is exercised systematically every day. A dog which has learned to beg before the operation recommences this practice quite spontaneously a week after a double-sided ablation of the motor zone.§ Occasionally, in a pigeon (or even, it is said, in a dog) we see the disturbances less marked immediately after the operation than they are half an hour later. This would be impossible were they due to the subtraction of the organs which normally carried them on. Moreover the entire drift of recent physiological and pathological speculation is towards enthroning inhibition as an ever-present and indispensable condition of orderly activity. We shall see how great is its importance, in the chapter on the Will. Mr. Charles Mercier considers that no muscular contraction, once begun, would ever stop without it, short of exhaustion

* Goltz: Pflüger's Archiv, vol. 8, p. 460; Freusberg: ibid. vol. 10, p. 174 Goltz: Verrichtungen des Grosshirns, p. 73.

Loeb Pflüger's Archiv, vol. 39, p. 276.

of the system;* and Brown-Séquard has for years been accumulating examples to show how far its influence extends. Under these circumstances it seems as if error might more probably lie in curtailing its sphere too much than in stretching it too far as an explanation of the phenomena following cortical lesion. ‡

corpora

On the other hand, if we admit no re-education of centres, we not only fly in the face of an a priori probability, but we find ourselves compelled by facts to suppose an almost incredible number of functions natively lodged in the centres below the thalami or even in those below the quadrigemina. I will consider the a priori objection after first taking a look at the facts which I have in mind. They confront us the moment we ask ourselves just which are the parts which perform the functions abolished by an operation after sufficient time has elapsed for restoration to occur?

The first observers thought that they must be the corresponding parts of the opposite or intact hemisphere. But as long ago as 1875 Carville and Duret tested this by cutting out the fore-leg-centre on one side, in a dog, and then, after waiting till restitution had occurred, cutting it out on the opposite side as well. Goltz and others have done the same thing. If the opposite side were really the seat of the restored function, the original palsy should have appeared again and been permanent. But it did not appear at all; there appeared only a palsy of the hitherto unaffected side. The next supposition is that the parts surrounding the cut-out region learn vicariously to perform its duties. But here, again, experiment seems to upset the hypothesis, so far as the motor zone goes at least; for we may wait till motility has returned in the affected limb, and then both irritate the

The Nervous System and the Mind (1888), chaps. III, VI; also in Brain, vol. xi. p. 361.

+ Brown-Séquard has given a résumé of his opinions in the Archives de Physiologie for Oct. 1889, 5me. Série, vol. 1. p. 751.

Goltz first applied the inhibition theory to the brain in his Verrichtungen des Grosshirns,' p. 39 ff. On the general philosophy of Inhibition the reader may consult Brunton's Pharmakology and Therapeutics,' p. 154 ff., and also Nature,' vol. 27, p. 419 ff.

§ E.g. Herzen, Herman u. Schwalbe's Jahres-bericht for 1886, Physiol Abth. p. 38. (Experiments on new-born puppies.

cortex surrounding the wound without exciting the limb to movement, and ablate it, without bringing back the vanished palsy.* It would accordingly seem that the cerebral centres below the cortex must be the seat of the regained activities. But Goltz destroyed a dog's entire left hemisphere, together with the corpus striatum and the thalamus on that side, and kept him alive until a surprisingly small amount of motor and tactile disturbance remained.† These centres cannot here have accounted for the restitution. He has even, as it would appear,‡ ablated both the hemispheres of a dog, and kept him alive 51 days, able to walk and stand. The corpora striata and thalami in this dog were also practically gone. In view of such results we seem driven, with M. François-Franck,§ to fall back on the ganglia lower still, or even on the spinal cord as the 'vicarious' organ of which we are in quest. If the abeyance of function between the operation and the restoration was due exclusively to inhibition, then we must suppose these lowest centres to be in reality extremely accomplished organs. They must always have done what we now find them doing after function is restored, even when the hemispheres were intact. Of course this is conceivably the case; yet it does not seem very plausible. And the a priori considerations which a moment since I said I should urge, make it less plausible still.

For, in the first place, the brain is essentially a place of currents, which run in organized paths. Loss of function can only mean one of two things, either that a current can no longer run in, or that if it runs in, it can no longer run out, by its old path. Either of these inabilities may come from a local ablation; and 'restitution' can then only mean that, in spite of a temporary block, an inrunning current has at last become enabled to flow out by its old path againe.g., the sound of 'give your paw' discharges after some

* François-Franck: op. cit. p. 382. Results are somewhat contradictory. + Pflüger's Archiv, vol. 42, p. 419.

Neurologisches Centralblatt, 1889, p. 372.

Op. cit. p. 387. See pp. 378 to 388 for a discussion of the whole question. Compare also Wundt's Physiol. Psych., 3d ed., 1. 225 ff., and Luciani u. Seppili, pp. 243, 293.

weeks into the same canine muscles into which it used to discharge before the operation. As far as the cortex itself goes, since one of the purposes for which it actually exists. is the production of new paths,* the only question before us is: Is the formation of these particular vicarious' paths too much to expect of its plastic powers? It would certainly be too much to expect that a hemisphere should receive currents from optic fibres whose arriving-place within it is destroyed, or that it should discharge into fibres of the pyramidal strand if their place of exit is broken down. Such lesions as these must be irreparable within that hemisphere. Yet even then, through the other hemisphere, the corpus callosum, and the bilateral connections in the spinal cord, one can imagine some road by which the old muscles might eventually be innervated by the same incoming currents which innervated them before the block. And for all minor interruptions, not involving the arrivingplace of the 'cortico-petal' or the place of exit of the 'corticofugal' fibres, roundabout paths of some sort through the affected hemisphere itself must exist, for every point of it is, remotely at least, in potential communication with every other point. The normal paths are only paths of least resistance. If they get blocked or cut, paths formerly more resistant become the least resistant paths under the changed conditions. It must never be forgotten that a current that runs in has got to run out somewhere; and if it only once succeeds by accident in striking into its old place of exit again, the thrill of satisfaction which the consciousness connected with the whole residual brain then receives will reinforce and fix the paths of that moment and make them more likely to be struck into again. The resultant feeling that the old habitual act is at last successfully back again, becomes itself a new stimulus which stamps all the existing currents in. It is matter of experience that such feelings of successful achievement do tend to fix in our memory whatever processes have led to them; and we shall have

The Chapters on Habit, Association, Memory, and Perception will change our present preliminary conjecture that that is one of its essential ses, into an unshakable conviction.

a good deal more to say upon the subject when we come to the Chapter on the Will.

My conclusion then is this: that some of the restitution of function (especially where the cortical lesion is not too great) is probably due to genuinely vicarious function on the part of the centres that remain; whilst some of it is due to the passing off of inhibitions. In other words, both the vicarious theory and the inhibition theory are true in their measure. But as for determining that measure, or saying which centres are vicarious, and to what extent they can learn new tricks, that is impossible at present.

FINAL CORRECTION OF THE MEYNERT SCHEME.

And now, after learning all these facts, what are we to think of the child and the candle-flame, and of that scheme which provisionally imposed itself on our acceptance after surveying the actions of the frog? (Cf. pp. 25-6, supra.) It will be remembered that we then considered the lower centres en masse as machines for responding to present senseimpressions exclusively, and the hemispheres as equally exclusive organs of action from inward considerations or ideas; and that, following Meynert, we supposed the hemispheres to have no native tendencies to determinate activity, but to be merely superadded organs for breaking up the various reflexes performed by the lower centres, and combining their motor and sensory elements in novel ways. It will also be remembered that I prophesied that we should be obliged to soften down the sharpness of this distinction after we had completed our survey of the farther facts. The time has now come for that correction to be made.

Wider and completer observations show us both that the lower centres are more spontaneous, and that the hemispheres are more automatic, than the Meynert scheme allows. Schrader's observations in Goltz's Laboratory on hemisphereless frogs* and pigeons † give an idea quite different from the picture of these creatures which is classically current. Steiner's observations on frogs

* Pflüger's Archiv, vol. 41, p. 75 (1887). Ibid., vol. 44, p. 175 (1889) Untersuchungen über die Physiologie des Froschhirns, 1885.