THE MIND AFFECTED BY THE BLOOD.

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the blood supplied to the brain. No organ is active without blood. The demand made by the brain corresponds with the extent and energy of its functions. Deficiency in the circulation is accompanied with feeble manifestations of mind. In sleep, there is a diminution of the supply of arterial blood to the brain. General depletion lowers all the functions generally, mind included. On the other hand, when the cerebral circulation is quickened, the feelings are roused, the thoughts are more rapid, the volitions more vehement; great mental exciternent is always accompanied with an unusual flow of blood, often outwardly shown by the throbbing of the vessels. In delirium, the circulation attains an extraordinary pitch

The blood must possess a certain quality, involving the presence of certain ingredients and the absence of others. Wholesome nourishment supplies the first condition of nervous and mental activity; inanition or starvation, feebleness of digestion, militate against the exercise of the mental functions. Moreover, the blood may be abundant and rich in nutritive matters, yet the organ of the mind. may be unduly depressed by the excessive drafts of the other interests of the system, as, for example, the muscles; under great muscular strain, there is very little capability of mental effort. Again, there are certain substances, known as stimulants, that are considered to supply the blood with an element specially provocative of nervous change; as alcohol, tobacco, tea, opium, &c.

The substances that must be absent include the so-called

poisons, and the impurities of the body itself, which several large viscera are occupied in removing. The chief of these impurities are carbonic acid and urea; either of them left to accumulate in the blood leads to mental depression, unconsciousness, and finally death. Hence the mental tone depends no less upon the vigorous condition of the purifying organs-lungs, liver, intestines, kidneys, skin -than upon the presence of nutritive material obtained from the food.

CHAPTER III.

THE CONNEXION VIEWED AS CORRESPONDENCE, OR

CONCOMITANT VARIATION.

THE dependence of one thing upon another, is ordinarily shown by two classes of facts-the first, the presence of the cause followed by the presence of the effect; the second, the absence of the cause followed by the absence of the effect as when we prove that lighting a fire is the cause of smoke, or oxygen the cause of putrefaction and decay. Of the two methods, the second-the absence of the cause followed by the absence of the effect-is the most decisive; the preservation of meat by excluding air is the best proof that air, or some ingredient of it, is the cause of putrefaction. More especially convincing is the abrupt removal of a supposed cause, leading at once to the suspension of an effect.

There are cases, however, where we cannot make the experiment of removing an agent. We cannot get away from the earth where we live. We cannot remove the moon from its sphere, so as to see what actions on the earth depend upon it; we cannot by an abrupt suspension of lunar gravitation prove that the tides are very largely dependent on lunar influence.

For such cases, recourse is had to a third expedient, which happily solves the difficulty, and furnishes the proof required. If the agency in question, although irremovable, passes through gradations whose amount can be measured, we are able to observe whether the effect has corresponding changes of degree; and if a strict concomitance is observable between the intensity of the cause and the intensity of the effect, we have a presumption that may rise to positive proof of the connexion. It is thus shown that the tides depend on the moon and the sun conjointly; that the gaseous and liquid states of matter are due to heat.

In such a question as the connexion of mind and body, the potent method of removing the cause is not applicable. We cannot dissect the compound, man, into body apart and mind apart; we cannot remove mind so as to see if the body will vanish. We may remove the body, and in so doing we find that mind has disappeared; but the experiment is not conclusive; for, in removing the body we remove our indicator of the mind, namely, the bodily manifestations-as if in testing for magnetism we should set aside the needle and other tokens of its presence.

Neither can the method of absence be employed upon the chief organ of mind-the brain. The removal of the brain is undoubtedly the extinction of the manifestations of mind, but it is also, except in very low organisms the extinction of the bodily life. Important results are gained by partial removal of the brain, and we can reason

SIZE OF BRAIN AND MENTAL POWER.

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from these to what would happen by removing the whole. This is the nearest approach we can make to the best form of experimental proof.

The method of Concomitance or Correspondence is, however, applicable to the full extent. We can compare the gradations of the brain and nervous system through the animal series, and observe whether there are like gradations in the powers of the mind.

A considerable time has elapsed since attention was called by phrenologists to the connexion between size of brain and mental development in human beings. The large heads of men distinguished for high intellectual endowments, or for great energy of character in other ways, have been contrasted with the small heads of idiots. The rule is not strictly maintained in every instance; occasionally a stupid man has a larger brain than a clever man. But these are only individual exceptions to a prevailing arrangement. When extensive statistics are taken, the conclusion is established that great mental superiority is accompanied with a more than average size of brain. The following is a table of the brain weights of several distinguished men :—