other in such a manner that those of the right side go to the left, and vice versa; that these bundles, after having been first dilated by an admixture of grey matter, and having formed the eminence called pons varolii, separate, and take the name of crura cerebri, continuing still to give origin to nerves; that they become dilated again by a new addition of grey matter, to form the masses called optic thalami, and a third time to form the corpora striata; that, from all, the external edge of these last dilatations, arises a plate of greater or less thickness according to the species, completely invested in grey matter, which turns upwards to cover them, forming what are called the hemispheres, and which, after being bent down in the middle, unite to that of the opposite side by one or more commissures or bundles of transverse fibres, the most considerable of which, peculiar to the mammalia, is called corpus callosum. It is known, besides, that on the crura cerebri behind the optic thalami are one or two pairs of smaller dilatations, known, when there are two pairs, as in the mammalia, by the name of tubercula quadrigemina, from the first of which the optic nerves seem to arise; that the olfactory nerve is the only one which does not apparently take its origin either from the medulla or its pillars; finally, that the cerebellum, white within and ash-coloured without, like the hemispheres, but often much more divided by external folds, is situated transversely behind the tubercula quadrigemina, and upon the medulla oblongata, to which it is united by transverse bundles, called crura cerebelli, which enter at the side of the pons varolii.

It was among these masses, so various and complicated, that it was necessary to seek the point from which irritation departed and the point where sensation arrives; it was their respective co-operation in acts of volition which was to be determined:such was the chief object of M. Flourens' investigations. He first examined how far up it was possible to go, still producing efficient irritation on the muscular system, and he found a point where these irritations remained ineffectual; then taking the brain at the opposite part, he irritated it at points deeper and deeper, as long as he did not act upon the muscles; and, when he did begin to act upon them, he found himself at the same point where the action had ceased in ascending. This part is also that where the sensation of irritation applied to the nervous system likewise ceases: above this, punctures and wounds do not excite pain. Thus M. Flourens pricked the hemispheres without producing contraction of the muscles, nor the appearance of pain in the animal; he removed them in successive slices: he did the same with regard to the cerebellum; he removed at once the hemispheres and cerebellum. The animal remained passive. The corpora striata and the optic thalami were at

tacked, and removed without any other effect: the iris was not contracted, nor even paralysed. But, when he pricked the tubercula quadrigemina, trembling and convulsions began, and these increased in proportion as he penetrated into the medulla oblongata. Pricking the tubercles, as well as the optic nerve, produced quick and continued contraction of the iris. These experiments agree with those of LORRY, published in the third volume of the Memoires des Savans étrangers.' "Neither the irritation of the brain nor of the corpus callosum itself produce convulsions: it may even be removed with impunity. The only part among those contained in the brain which has appeared uniformly and universally capable of exciting convulsions, is the medulla oblongata: it is this part which produces them to the exclusion of every other." They contradict the experiments of Haller and Ziun with regard to the cerebellum; but, from what M. Flourens has seen and pointed out, it appears that these physiologists had touched the medulla without being aware of it. The author concludes that the medulla oblongata and the tubercles are (in his language) irritable; which in ours means that they are conductors of irritation, like the spinal marrow and nerves, but that neither the cerebrum nor cerebellum possess this property. The author hence concludes, likewise, that these tubercles form the continuation and superior termination of the spinal cord and medulla oblongata; and this opinion is in conformity with their situation and anatomical connexions.

Wounds of the brain and cerebellum do not excite pain any more than convulsions, and, in ordinary language, we would say that both are insensible: but M. Flourens, on the contrary, says that these are the sensible parts of the nervous system; which means simply that it is to them the impression received by sensible organs must be conveyed, in order that the animal may experience a sensation. M. Flourens appears to have esta blished this proposition in a satisfactory manner, with regard to the senses of sight and hearing. When the cerebral lobe of one side is removed, the animal does not see with the eye of the opposite side, although the iris of this eye retains its mobility: when both lobes are removed, he becomes both blind and deaf. But it does not appear that he has shown it equally well in respect to the other senses. First, he has not, and could not make, any experiment upon smell or taste; and, even with regard to touch, the experiments are unsatisfactory. Indeed, the animal, thus mutilated, assumes the appearance of stupor: he has no longer any will of his own, and performs no voluntary movement; but, when he is struck or pricked, he affects the gait of an animal which awakes: in whatever position he is placed, he resumes

his equilibrium. If laid on the back, he rises; if pushed, be walks. A frog leaps when touched; a bird flies if thrown into the air,-it struggles if annoyed,—if water be poured into the beak, it swallows. Without doubt, one can scarcely suppose all these actions to take place without being excited by some sensation. Certainly they are not guided by reason: the animal escapes without object; he has no longer any memory; he strikes himself many times against the same obstacle: but this proves at most (indeed it is the expression of M. Flourens himself,) that such an animal is in a state of sleep. But we are far from thinking that a man who is asleep when he moves, and takes a more convenient position, is altogether deprived of sensation; and, although the perceptions have not been distinct, and although he has not preserved the recollection of them, this is no proof that he has not experienced them. Thus, instead of saying, with the author, that the cerebral lobes are the only organs of sensation, we would restrict ourselves to ascertained facts, and content ourselves with saying that these lobes are the sole receptacle where the senses of sight and hearing can be perfected, and become perceptible to the animal. If we wished to add to this, we would say that they are likewise those where all the sensations take a distinct form, and leave durable traces on the memory,-that they serve, in a word, as the seat of memory; a property, by means of which they furnish the animal with materials for judgment. This conclusion, thus reduced to proper terms, becomes the more probable, in that, besides the verisimilitude which it receives from the structure of these lobes and their connexion with the rest of the system, comparative anatomy offers another confirmation in the constant relation of the volume of these lobes with the degree of intelligence of the animal.

After the effects of ablation, properly so called, M. Flourens examines those of the extirpation of the tubercula quadrigemina. The removal of one of them, after a convulsive movement, which soon ceases, produces, as a permanent result, blindness of the opposite eye and involuntary staggering, (tourniement;) that of both tubercles renders the blindness complete, and the staggering more violent and long-continued. The animal, however, retains all its faculties, and the iris continues contractile. The deep extirpation of the tubercle, or the section of the optic nerve only, paralyzes the iris: from which the author infers, that the ablation of the tubercle only acts as the division of the nerve would do; that this tubercle is only a conductor with regard to vision; and that the cerebral lobe alone is the seat of the sensation, the point where it is consummated, and passes into perception. It is necessary to remark, besides,

that, in pushing this extirpation of the tubercles very deep, the medulla oblongata becomes concerned, which gives rise to violent and long-continued convulsions.

The part of the author's investigations which possess most characters of interest and novelty, relates to the functions of the cerebellum. During the ablation of the first layers, there appeared only a slight weakness and want of harmony among the movements. At the middle layers, a disturbance nearly general was manifested. The animal, in continuing to see and hear, only executed quick and irregular movements: the faculty of flying, walking, and keeping itself standing, were lost by degrees. When the brain was cut off, this faculty of performing regulated motions had entirely disappeared. Placed upon the back, he did not rise; but continued to see the blow which menaced him; he heard sounds, and endeavoured to shun the danger which was threatened: in a word, feeling and volition were retained, but the power over the muscles was lost; scarcely could he support himself with the assistance of the wings and tail. In depriving the animal of the brain, it was thrown into a state resembling sleep: in removing the cerebellum, it was brought to a state resembling intoxication. "It is surprising," says M. Flourens, "to see the pigeon, in proportion as it loses the cerebellum, gradually lose the power of flying,-then that of walking, and, lastly, that of standing: this last is only lost by degrees. The animal begins by being no longer able to keep its balance on the legs; then the feet do not suffice to support it, and next every fixed position becomes impossible; it makes incredible efforts to assume some particular position, without effecting it not withstanding, when exhausted with fatigue, it appears to wish for repose. Its senses were so much alive, that the slightest gesture made it begin its contortions anew, without the smallest degree of convulsive action being induced, as long as the medulla oblongata and tubercula quadrigemina were left untouched."

(The reporters seem to have supposed these experiments without any precedent in physiological record; but, in a note by the writer in the Journal Complementaire for March, reference is made to a work by M. ROLANDO, in which similar experiments are described. The inferences, however, drawn by the Italian physiologist, differ in this-that he regarded the cerebellum, not as the regulator, but as the source of locomotion.)

Experiments on the cerebellum of quadrupeds, particularly adults, are extremely difficult, on account of the large portions of bone it is necessary to remove, and the great vessels which require to be cut. The greater number of experimentalists operated after some plan already known, and, for the most part,

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have been too ready to see what they intended; and assuredly no one has heretofore suspected that the cerebellum was in some manner the regulator of locomotion. This discovery, if repeated experiments, made with necessary precaution, should establish it as a general law, must reflect the highest honour on the young physiologist whose work we have analyzed...

The integrity of the cerebral lobes is necessary to the exercise of sight and hearing: when they are removed, the will no longer manifests itself by voluntary acts. However, when the animal is immediately excited, he performs regular movements, as if endeavouring to avoid pain or inconvenience; but these movements do not effect his purpose, most probably because the memory, which has been removed along with the lobes which constituted its seat, no longer afford grounds or elements of judgment: these movements have no consistency, for the same reason, that the impulse which caused them neither leaves any remembrance nor permanent volition. The integrity of the cerebellum is necessary to the regularity of locomotion: let the brain remain, the animal will see, hear, and have evident and powerful volition; but, if the cerebellum be removed, he will never find the balance necessary to locomotion. As to the rest, irritability remains in parts without the brain or cerebellum being necessary. Every irritation of a nerve brings it into play, in muscles to which it is distributed: every irritation of the spinal marrow excites it in all the members beneath the point of its application. It is quite at the top of the medulla oblongata, at the point where the tubercula quadrigemina joins it, that this faculty of receiving and propagating irritation on the one band, and pain on the other, ceases. It is this point at which sensation must arrive in order to be perceived: it is from hence that the mandates of the will must emanate. Thus, the continuity of the nervous organ from this point to the parts is requisite for voluntary motion, and for the perception of impressions, whether external or internal.

All these conclusions are not identical with those of the author, and still less are they expressed in the same terms; but they are such as have appeared to the reporters to result from a rigorous examination of the facts he has established.