remarkable absence of the effects manifested in the other centres. Neither feeling nor movement is produced. This marks a very great distinction between the hemispheres and the whole of the ganglia and centres lying beneath them.

The entire removal of the hemisphere including the corpus striatum and thalamus, lowers the power of the animal, but does not destroy any of the bodily or mental functions.

Pressure from above downwards produces stupor.

The removal of both hemispheres in an animal has the following results :—

First. Sight and hearing are entirely lost.

Second. Consciousness, or feeling, seems utterly abolished: so that whatever bodily activity may survive, the mental life is extinct.

Third. All power of moving for an end, all forethought, purpose, or volition, is entirely extinguished. This is an inevitable consequence of the loss of feeling; for with feeling, the actions stimulated or guided by feeling must disappear.

Fourth. The power of accomplishing many connected movements still remains. The actions of flying or walking may be sustained after the loss of the hemispheres, but in that case a stimulus from without is necessary in order to commence the action. As a matter of course the Automatic actions, those that we have seen to go on in the decapitated or acephalous animal may still proceed.

Thus it appears that the hemispheres of the brain are indispensable to the exercise of our two highest senses, and to consciousness and feeling-prompted action, or volition. In so far as Intelligence demands the exercise of those functions, it, too, must perish. The actions that remain are at best the actions of a somnambulist. Mind is thus pre-eminently associated with the cerebral hemispheres.

Functions of the Cerebellum.

21. The experiments made upon the cerebellum, and the inferences founded on its comparative size in different animals, have led physiologists to assign to it the function of harmo

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nizing and co-ordinating the locomotive movements. When an action becomes complex, that is, demands the exercise of several groups of muscles in a fixed order and alternation, the due performance of the act must be provided for by some organization of the nerve centres. We have already seen that the medulla oblongata can support the two-stroke movement of the lungs; but there are still higher complexities to be provided for. The act of walking of a biped, for example, is at the very least a four-stroke movement, since there must be an impulse to and fro for either limb; and if these four strokes did not succeed in due harmony, the animal would be at a stand-still. Walking on all fours is still more complicated, demanding at least eight motions to be harmonized. The operation of chewing is another case in point; there is a complicated concurrence of movements of the jaw, the tongue, and the cheeks; and if any one of these make a false step, some accident, such as the biting of the tongue will result. In man the actions of the hand and fingers are extremely complex. The movements connected with the maintenance of the erect posture are likewise very numerous, so much so that a long education is needed for their due performance. To as many of these actions as are primitive, or instinctive, the cerebellum would appear to be an indispensable support, and so doubtless it must be to the acquired actions based on them. The following quotation from Messrs. Todd and Bowman, will exhibit the experimental proofs of this function.

'Flourens removed the cerebellum from pigeons by successive slices. During the removal of the superficial layers there appeared only a slight feebleness and want of harmony in the movements, without any expression of pain. On reaching the middle layers, an almost universal agitation was mani_ fested, without any sign of convulsion; the animal performed rapid and ill-regulated movements; it could hear and see. After the removal of the deepest layers, the animal lost completely the power of standing, walking, leaping, or flying. The power had been injured by the previous mutilations, but now it was completely gone. When placed upon his back, he was unable to rise. He did not, however, remain quiet and

motionless, as pigeons deprived of the cerebral hemispheres do; but evinced an incessant restlessness, and an inability to accomplish any regular or definite movement. He could see the instrument raised to threaten him with a blow, and would make a thousand contortions to avoid it, but did not escape. Volition and sensation remained, the power of executing movements remained; but that of co-ordinating these movements into regular and combined actions was lost.

'Animals deprived of the cerebellum are in a condition very similar to that of a drunken man, so far as relates to their power of locomotion. They are unable to produce that combination of action in different sets of muscles which is necessary to enable them to assume or maintain any attitudes. They cannot stand still for a moment, and in attempting to walk, their gait is unsteady, they totter from side to side, and their progress is interrupted by frequent falls. The fruitless attempts which they make to stand or walk are sufficient proof that a certain degree of intelligence remains, and that voluntary power continues to be enjoyed.' (T. and B., 359.)

When the cerebellum is cut away at the top, the animal moves backward. When one side is cut away, the animal rolls over to the injured side. Sometimes a vertiginous action ensues, as if the body were revolved on a spit.

We have reason to suppose that dexterity and precision of movements, manual or other, are connected with a well developed cerebellum.

The phrenologists have attributed to the cerebellum the sexual function, with the amatory feelings corresponding thereto; but the greater number of physiologists are decidedly opposed to this view.

The white matter of the brain, which performs those incessant and innumerable acts of communication between the central masses, is thus not less important than the grey matter where force originates. Accordingly, we find that in the higher animals, the white substance becomes developed in proportion to the energy of the mental functions. As we descend the scale, the white matter dwindles in a most notable way: in birds, the grand junction of the brain, the pons Varolii, disappears as

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a distinct mass; and down to reptiles and fishes, the same course of diminution is seen to proceed.

Of the Nerve Force and the course of Power in the Brain.

22. The structure of the nervous substance, and the experiments made upon the nerves and nerve centres, establish beyond doubt certain peculiarities as belonging to the force that is exercised by the brain. This force is of a current nature; that is to say, a power generated at one part of the structure is conveyed along an intervening substance, and discharged at some other part. The different forms of Electricity and Magnetism have made us familiar with this sort of action. In a voltaic cell, an energy is gendered and transmitted along a wire with inconceivable rapidity to any place where the conductor reaches. The telegraph wire, as already said, bears a strong resemblance to a nerve passing from the brain to any part of the body; and the grey substance of the nerve centres, which are highly supplied with blood, is paralleled by the voltaic battery where the electric power is generated by the corroding power of an acid.

This portable, or current, character of the nerve force is what enables movements distant from one another in the body to be associated together under a common stimulus. An impression of sound, a musical note, for example, is carried to the brain; this impression is seen to produce a responsive action and excitement extending to the voice, mouth, eyes, head, &c. This multiplex and various manifestation implies a system of connexion among the centres of action, whereby many strings can be touched from one point; a connexion due to the conducting nerves that pass and repass from centre to centre, and from the centres to the muscular apparatus over the body. Supposing the corpora quadrigemina to be a centre for the sense of vision, an impression passing to this centre propagates a movement towards many other centres,—to the convoluted hemispheres upwards, to the cerebellum behind, and to the medulla oblongata and spinal cord beneath; and through these various connexions an extensive wave of effects

may be produced, ending in a complicated chain of movements all over the framework of the body. Such a system of intercommunication and transmission of power is therefore an essential part of the bodily and mental structure.

23. The analogy that exists between nerve power and electricity does not amount to identity. The nerve force is not either electricity or magnetism. The differences between the two are broad and distinct. The following is a statement of some of those differences.

In the first place, in the development of voltaic electricity a closed circuit is indispensable. The influence generated in the cell cannot pass along the conducting wire until a complete circle of wire or other conducting material is made, bringing the influence round to the cell again. The moment the circuit is interrupted, the power ceases. But no such closed circuit can be traced in the nervous apparatus. An influence arising from a centre may pass out into a muscle and be discharged there, without any return influence that can at present be traced. It has been seen that in the experiments on the nerves, by mechanical or other irritation, there is no necessity for a completed circuit. Nervous power requires the connexion of a centre with fibrous communications to distant parts, but does not appear to demand a perfect circle of nerves. Grey matter alone can do nothing; a combination of grey with white, or of central with conducting power is always requisite, but a single outgoing thread terminating in a limb, would seem to suffice for the effect. We do not, however, include the kind of circle completed in reflex actions, which is quite different in its nature from the circle here discussed.

In the second place, the conducting power of nerve fibre is a wasting operation, one that draws upon the vitality of the fibre, and causes the necessity for times of rest and a copious supply of nourishment. The common experience of nervous fatigue and exhaustion is a proof of this. We have no good grounds for limiting the locality of nervous exhaustion to the grey matter alone. The nerve fibres are richly supplied with