LAW OF RELATIVITY.

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With reference to many of our feelings, mankind have always to some extent recognized the working of this principle. It is seen that the first shock of the transition from one state to another-from sickness to health, poverty to abundance, ignorance to knowledge—is the most intense, and that as the memory of the previous condition fades away, so does the liveliness of the emotion caused by the change. Leisure, retirement, rest, are enjoyed only by contrast to previous toils. The incessant demands for novelty and change, for constant advances in wealth, in knowledge, in the arrangements of society, farther show the principle of Relativity as applied to pleasure.

Language contains many names avowedly relative, as parent, child; ruler, subject; up, down; north, south; light, dark; virtue, vice. It is obvious that either name in those couples implies the other; there can be no ruler without a subject. But, in reality, the principle of Relativity applies to everything that we are capable of knowing. Whatever we can conceive implies some other thing or things also conceivable, the contrast, co-relative, or negative of that. Red means the exclusion of all the other colours. If we had never been affected by any colour except red, colour would never have been recognized by us. When we speak of a fixed star, we mean to exclude certain other things-the sun, planets, comets, &c. When we make an affirmation, the stars shine by their own light,' we also by implication make a denial, 'the stars do not borrow their light.'

The applications of this principle are numerous and important. It bears directly on the arts of human happiness; it is essentially involved in Fine Art; it must be attended to in the communication of knowledge; in Metaphysics it conflicts with the doctrine of the Absolute. (For farther remarks on the Definition and Divisions of Mind, see APPENDIX A.)

1. A

CHAPTER 11.

THE NERVOUS SYSTEM.

LTHOUGH Subject and Object (Mind and Matter) are

the most diametrically opposite facts of our experience, yet there is a concomitance or connexion between mind and a material organism. This position is best supported by the subsequent details. (See also APPENDIX B.)

The parts of the human frame that chiefly concern the student of mental science are the Nerves and Nerve Centres (principally collected in the Brain), the Organs of Sense, and the Muscular System. The organs of sense and of movement will be described afterwards; a brief description of the Nerves and Nerve Centres will occupy this preliminary chapter, in which we shall confine ourselves as far as possible to the facts bearing directly or indirectly upon Mind.

2. That the Brain is the principal organ of Mind is proved by such observations as the following:

(1.) From the local feelings that we experience during mental excitement. In most cases of bodily irritation, we can assign the place or seat of the disturbance. We localize indigestion in the stomach, irritation of the lungs in the chest, toothache in the gums or jaws; and when the mental workings give rise to pain, we point to the head. In ordinary circumstances we have no local consciousness of mental action, but in a time of great mental agitation, or after any unusual exertion of thought, the aching or oppression in the head tells where the seat of action is, precisely as aching limbs prove what muscles have been exercised during a long day's march. The observation can occasionally be carried much farther; for it is found that a series of intense mental emotions, or an excessive strain on the powers of thinking, will end in a diseased alteration of the substance of the brain.

THE BRAIN THE ORGAN OF MIND.

11

(2.) Injury or disease of the brain impairs in some way or other the powers of the mind. A blow on the head will

destroy consciousness for the time; a severe hurt will cause a loss of memory. The various disorders of the brain, as inflammation, softening, &c., are known to affect the mental energies. Insanity is often accompanied by evident cerebral disease.

(3.) The products of nervous waste are increased when the mind is more than ordinarily exerted. The alkaline phosphates (triple phosphate of ammonia and magnesia) removed by the kidneys are derived principally from the waste of nervous substance; and they are sensibly increased after great mental exertion or excitement. Phosphorus

abounds more in the brain than in any other tissue.

(4.) There is an indisputable connexion between size of brain and the mental energy displayed by the individual man or animal. It cannot be maintained that size is the sole circumstance that determines the amount of mental force. But just as largeness of muscle gives greater strength of body, as a general rule, so largeuess of brain gives greater vigour of mental impulse. The measurements of the heads of remarkable men have often been quoted. 'All other circumstances being alike,' says Dr. Sharpey, 'the size of the brain appears to bear a general relation to the mental power of the individual,—although instances occur in which this rule is not applicable. The brain of Cuvier weighed upwards of 64 oz., and that of the late Dr. Abercrombie about 63 oz. avoirdupois. On the other hand, the brain in idiots is remarkably sinall. In three idiots, whose ages were sixteen, forty, and fifty years, Tiedemann found the weight of their respective brains to be 193 oz., 25 oz., and 221 oz.; and Dr. Sims records the case of a female idiot twelve years old, whose brain weighed 27 oz. The weight of the human brain is taken at about 3 lbs. (48 oz.).'—QUAIN'S Anatomy, Vol. II., p. 432.*

In a paper by Mr. John Marshall, of University College, read before the Royal Society (June, 1863), the author gives a minute account of

(5.) The specific experiments on the nerve cords and nerve centres, to be afterwards quoted, have proved the immediate dependence of sensation, intelligence, and volition on those parts.

No fact in our constitution can be considered more certain than this, that the brain is the chief organ of mind, and has mind for its principal function. As we descend in the animal scale, through Quadrupeds, Birds, Reptiles, Fishes, &c., the nervous system dwindles according to the decreasing measure of mental endowment.

three brains, one the brain of a Bushwoman, the others the brains of two idiots of European descent. The Bushwoman's brain was computed to have weighed in the fresh state 31 oz. One of the idiots was a woman aged forty-two years; she was able to walk, though badly, to nurse a doll, and to say a few words; the weight of her brain was 10 oz. 5 grs. The other was a boy of twelve; he could neither walk nor handle anything, nor articulate a single word; the weight of his brain was 8 oz. These are the two smallest idiot brains whose weight has been recorded.

Mr. Marshall enters into a very minute description of the structure of all the three brains, and his remarks are valuable as showing what other deficiencies, besides weight, attach to the brains of human beings of low mental power. Not merely is the cerebrum in idiots a small organ, having all the proper parts on a smaller scale, but these parts are fewer in number, less complex, and different in relative proportion and position. And in particular, the convolutions of the brain are much less developed, much simpler, than in an average brain. On comparing the two idiots in question, the convolutions of the woman were more developed than those of the boy.

The circumstance of inequality in the richness of the convolutions has been alluded to by physiologists as explaining the cases of great mental power allied with brains not above the average weight. Such differences have actually been observed in the examination of brains. The brain of Cuvier was said to be distinguished in this respect, as well as in weight. But the connexion of force of mind with richness of convolutions is also liable to various qualifications. It does not hold in the comparison of different species, -the sheep's brain is more highly convoluted than the dog's; and there are well authenticated cases of men of superior powers, whose brains, both as to weight and as to convolutions, were below the average. Still, there can be no doubt that generally, though not universally, an increase in one or both of these peculiarities is the concomitant of a higher mental endowment. Both the statistics of the Races of men, and Comparative Anatomy, are decisive to this extent.

We may readily suppose that, with a view to intellectual power, an abundance of nervous elements-fibres and corpuscles-must be accompanied with a felicitous distribution or arrangement of them.

DIVISIONS OF THE NERVOUS SYSTEM.

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3. The NERVOUS SYSTEM consists of a central part, or rather a series of connected central organs named the cerebrospinal axis, or cerebro-spinal centre; and of the nerves, which have the form of cords connected at one extremity with the cerebro-spinal centre, and extending from thence through the body to the muscles, sensible parts, and other organs placed under their control. The nerves form the medium of communication between these distant parts and the centre; one class of nervous fibres, termed afferent (incarrying) or centripetal, conducting impressions towards the centre,― another, the efferent (outcarrying) or centrifugal, carrying inaterial stimuli from the centre to the moving organs. The nerves are, therefore, said to be internuncial in their office, whilst the central organ receives the impressions conducted to it by the one class of nerves, and imparts stimuli to the other, rendering certain of these impressions cognizable to the mind, and combining in due association, and towards a definite end, movements, whether voluntary or involuntary, of different and often of distant parts.'-QUAIN, Introduction.

The foregoing division of the nervous system into nervecentres and nerve-cords determines the order and method of description both as regards their Anatomy, or structure, and their Physiology, or function.

THE NERVOUS SUBSTANCE,

4. The nervous system is made up of a substance proper and peculiar to it, with inclosing membranes, cellular tissue, and blood vessels. The nervous substance has long been distinguished into two kinds, obviously differing from each other in colour, and therefore named the white, and the grey, or cineritious (ashcoloured).

'When subjected to the microscope, the nervous substance is seen to consist of two different structural elements, viz., fibres, and cells or vesicles. The fibres are found universally in the nervous cords, and they also constitute the greater part of the nervous centres; the cells or vesicles, on the other hand, are confined in a great measure to the latter, and do not exist in the nerves properly so called, unless it be at their peripheral expansions in some