ORDER OF EXPOSITION.

the ultimate properties and the fundamental classification of mind, we do not propose that the exposition should proceed strictly in the order in which those are stated.

Although Emotion and Volition, in their elementary aspect, can be explained before entering on the consideration of the Intellect, while one large important department of Emotion, namely, Sensation, is always considered as introductory to the Intellectual powers, yet the full exposition of the emotions and active impulses of our nature properly comes last in the systematic arrangement of the subject of mind. This exposition I do not enter upon in my present treatise.

CHAPTER II.

I.

OF THE NERVOUS SYSTEM.

THE connexion of the mental processes with certain of

the bodily organs is now understood to be of the most intimate kind. A knowledge of the structure of those organs may therefore be expected to aid us in the study of mind. The contribution at present obtained from this source is something considerable; which makes it not improper to introduce a small portion of the Anatomy and Physiology of the human body into the present work. 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 movement will fall to be described in Book First; 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 upon Mind, introducing only such further explanations as may be needed to make those facts clear and evident.

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 localise 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 the action of the brain is unconscious, but in a time of great mental agitation, or after any unusual exertion of thought, the aching or oppression within the skull tells where the seat of action is, precisely as aching limbs prove what

THE BRAIN AND THE MIND.

11

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 action of the powers of thinking, will end in a diseased alteration of the substance of the brain.

(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 for example, softening, &c., are known to affect the mental energies. Insanity is often accompanied by palpable disease of the cerebral substance, as shown by outward symptoms during life and by dissection after death.

(3.) The products of nervous waste are increased when the mind is more than ordinarily exerted. It is ascertained that the kidneys are mainly concerned in removing from the blood the saline and other matters arising from the waste of nervous substance; and it is well known that the secretions from the kidneys are greatly increased in times of mental excitement. Chemical analysis proves that the products on such occasions are derived from the nervous 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 only circumstance that determines the amount of mental force; quality is as important as quantity, whether in nerve, muscle, or any other portion of the animal structure. But just as largeness of muscle gives greater strength of body as a general rule, so largeness of brain gives greater vigour of mental impulse. The facts proving the large size and great weight 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 small. In three idiots, whose ages were sixteen, forty,

and fifty years, Tiedemann found the weight of their respective brains to be 19 oz., 25 oz., and 22 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, 5th edition, p. 671.

(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.

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 by 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 (in-bringing) or centripetal, conducting impressions towards the centre,another, the efferent (out-carrying) or centrifugal, carrying material 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.

Being contained partly within the head, and partly within the spine, or back-bone.

THE NERVOUS SUBSTANCE.

13

'Besides the cerebro-spinal centre and the nervous cords, the nervous system comprehends also certain bodies named ganglia, which are connected with the nerves in various situations. These bodies, though of much smaller size and less complex nature than the brain, agree, nevertheless, with that organ in their elementary structure, and to a certain extent also in their relation to the nervous fibres with which they are connected; and this correspondence becomes even more apparent in the nervous system of the lower members of the animal series. For these reasons, as well as from evidence derived from experiment, but which, as yet, it must be confessed, is of a less cogent character, the ganglia are regarded by many as nervous centres, to which impressions may be referred, and from which motorial stimuli may be reflected or emitted; but of local and limited influence as compared with the cerebro-spinal centre, and operating without our consciousness and without the intervention of the will.'-QUAIN, Introduction, p. clxxxvii.

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.

OF THE NERVOUS SUBSTANCE.

4. For the full details of the structure of nerve, as regards both the ultimate elements of cell and fibre and the masses made up of these elements, reference must be had to the best works on Anatomy. In the present state of our knowledge the entire significance of these details cannot be assigned; Physiology on the one hand, and mental science on the other, must be in a more advanced condition in order to make out such significance. Nevertheless there are certain leading features of the nerve structure that are even now of interest in the study of mind. I quote again from Dr. Sharpey's contributions to the 5th edition of QUAIN'S Anatomy.

'The nervous system is made up of a substance proper and peculiar to it, with inclosing membranes, cellular tissue, and