Oftentimes when the brain is abnormally excited, as in fevers, the dreaming state may be so active that the senses become subservient to the delusions. The patient believes in the presence of things which have no existence: he sees and hears from his brain without the visual or auditory organs. No amount of persuasion will convince him that his room is not occupied by persons with whom he holds an imaginary, to him a real, conversation. During delirium tremens the same delusions and spectral illusions take place; the brain's abnormal activity is so great as to project the dreamy illusive condition, so that the patient is haunted with companions whose existence is only the result of irregular or disordered function. It was this diseased condition of brain, producing such deceptive images, which led to the discovery, by the author, of Induced Mental Hallucination, or electro-biology; a state of brain corresponding most faithfully to that just cited.

No matter how inconsistent, irrational, or incongruous the subject, it is believed most implicitly during the period of the brain's abnormally induced state to be the truth. Vide Mental Hallucination.

We come into the world with inherent organic predispositions: that is, our brains are fashioned to receive one class of things in preference to another; one brain, from heritage, climate, geographical position, has certain natural capacities which may not exist in another. It is not to be supposed that the primitive education or surroundings of our earliest days do not modify and shape our future modes of thought; it is impossible to master or entirely stamp out the impressions of early youth. These are the basis on which all brain function is subsequently associated.

A strong emotion or impression in after life, either of grief or joy, of such serious import as to disturb our domestic relationship, as the loss of a beloved parent, or the unexpected possession of fortune's favours, will often so indelibly be photographed on the brain as to become the permanent basis of our future dreams. It is these violent mental shocks which make such a lasting impression on the brain, so that the least disturbing cause during sleep will provoke the most horrid or the most ecstatic dreams, with a vividness and power which leaves the brain unconsciously depressed or exalted during the waking state. Sometimes when during the dream we have been deceived and tantalized in our dearest affections, and our most cherished hopes blighted and crushed, the brain is left in a state of nervous exhaustion, and it is with great difficulty that any mental effort demanding a high order of thought can be exercised by the brain until a restoration has been established by "Nature's sweet restorer, balmy sleep;" but it must be undisturbed by dreams.

The functional exercise of any organ demands the expenditure of nervous force or fluid; the completeness or efficacy of these functions is always regulated by the supply of this nervous fluid. A superabundant, as well as a deficient supply, is equally prejudicial to healthy function. In the one case we have aberrations, hallucinations, mania, neuralgia; in the other, lethargic mentality, or even idiocy.

The remarkable case given of Mr. Gourlay's continued sleeplessness is illustrative of the one, and that of Cornelius Vromann's continued sleep of the other; they are antagonistic states of the nervous system. What was at first an abnormal state, by constant use or habitude, becomes eventually a normal function; verifying the old adage, that "use is second nature."

The condition which at first would have endangered life itself, if suddenly applied, is repelled at first with abhorrence; but by constant and gradual use the organs establish and adapt their functional exercise; and there is an accommodation to the new condition which actually becomes by this constant use essential to existence; for if too suddenly abandoned, the most serious results may follow.

No matter how large and beautifully proportioned the brain, it must be adequately supplied with nervous fluid, otherwise its functions are sluggish, wanting in mental power. A small brain of good quality, well supplied with its executive element, is far superior to one of large dimensions of coarse structure with an insufficient supply. A large brain must be associated with correspondingly large lung capacity, not alone mere size, for the respiratory condition differs in persons of different temperament. It is not to be imagined that the possession of a large respiratory apparatus necessarily implies a corresponding power of producing nervous fluid; in persons of lymphatic temperament there is an absence of intensity which is characteristic of the nervo-sanguineous temperament.

Quality more than compensates for want of quantity; in fine, quantity is a decided disadvantage if unaccompanied by quality. Under no circumstances can a coarse textured brain compete with one whose fibres are fine and closely, compactly, and densely arranged.

The examination microscopically of over 100 brains of Negroes, Indians, Chinese, has shown that these in the various degrees of texture are inferior to the European; in comparing the brain of the pure Negro with that of the Turk, there is as much difference as between pine and boxwood; the one being loosely held together, whereas the fibres of the other are closely compacted.

All animal fibres differ in as marked a degree. Compare the fibres of some fish and the muscles of the vulture or the eagle. Still both serve for the locomotion of the animal.

The density, firmness, and fineness of the brain is a criterion, every other condition being equal, as a measure of mental power. As a rule, all parts of the body co-ordinate in point of quality; it seldom happens that a dense brain in health co-exists with flabby muscles.

A leading journal in writing of the crews of the University boat-race of 1871, says: - "The Oxford eight is manned by a heavy set of men, "powerful so far as mere strength is concerned. The Cambridge crew, "on the other hand, are devoid of roughness, compact and work well to"gether; they never seem distressed, no matter what test they are put "to." This description exemplifies the difference between quantity and quality. No physiologist after reading this graphic description would have betted on Oxford; in fine, he would have given odds in favour of the compact Cambridge crew, which the result justified. The smaller crew had the quality of structure, which enabled them to sustain a prolonged effort without fatigue; thus endurance does not belong to mere size.

Every state of brain exhibits its corresponding effects; every phase of existence, from the earliest period of childhood to decrepit old age, has a corresponding condition of brain. The eye of the eagle can gaze at the sun, but that of the owl is dazzled and blinded by its light. Still they are both visual organs, each adapted to the particular sphere of functional exercise. So with the brains of the various forms of living matter, from the simplest ganglion to that of the highest development in civilized man. It is evident that these developments have been consequent on the chemical or telluric state of the earth itself at the various stages of its existence; all the modifications of life are marked and defined in the various zones of the planet, which is continually undergoing changes. From this cause have been brought into existence the successive grades of organization. The lowest forms of life are not prejudiced by a higher state, fitted for the existence of superior organizations. These are found in all parts of the earth's surface, in the full exercise of their reproductive functions, as they were at the earliest periods. If, however, a lower condition or change should temporarily take place, then the higher would become extinct.

As the changes of the earth's state of vitality have been inconceivably gradual, covering unnumbered ages, so have the distinct developments been brought into being, as distinct creations, each specially of its type, genus, order, or family. These may have been modified by the constant changes of the vital element emanating from the earth itself in combination with solar influence. There was a period when the Crustacea alone could exist; so there was a time when the different types of monkey, according to the special zone, were brought into existence. No doubt this was immediately prior to the period when the lowest types of man had first a habitation on the globe. It may be that the earth's creative function, in the production of animal life, has passed. It is impossible for our faculties to define a state of creative function. But if under certain favourable combinations the minutest and most simple forms of life are now brought into existence, it is not unphilosophical to infer that the creative condition of nature, under correspondingly favourable states, could not have produced a mammoth or a whale.