when renovation has set in, the organs generally are invigorated. This is the first and most obvious consequence. It has next to be qualified by the remark that human beings are unequally constituted as regards the various functions; some being strong in muscle, others in stomach, others in brain. In all such persons the general invigoration is unequally shown; the favored organs receive a share proportioned to their respective capitals: to him that hath shall be given. Still more pertinent is the further qualification, that the organ that happens to be most active at the time receives more than its share; to exercise the several organs unequally is to nourish them unequally.
To come to the point as regards our immediate object. To increase the plastic property of the mind you must nourish the brain. You naturally expect that this result will ensue when the body generally is nourished: and so it will, if there be no exorbitant demands on the part of other organs, giving them such a preference as to leave very little for the organ of the mind. If the digestion or the muscles are unduly drawn upon, the brain will not respond to the drafts made upon it. Obversely, if the brain is so constituted by nature, or so excited by stimulation, as to absorb the lion's share of the nutriment, the opposite results will appear; the mental functions will be exalted, and the other interests more or less impoverished. This is the situation for an abundant display of mental force.
But we must further distinguish the mental functions themselves; for these are very different and mutually exclusive. Great refinement in the subdivisions is not necessary for the illustration. The broadest contrast is the emotional and the intellectual—feeling as pleasure, pain, or excitement, and feeling as knowledge. These two in extreme manifestation are hostile to each other: under extreme emotional excitement the intellect suffers; under great intellectual exertion the emotions subside (with limitations unnecessary for our purpose).
But intellect in the largest sense is not identical with the retentive or plastic operation. The laws of this peculiar phase of our intelligence are best obtained by studying it as a purely mental fact. Yet there is a physiological way of looking at it that is strongly confirmative of our psychological observations. On the physical or physiological side, memory or acquisition is a series of new nervous growths, the establishment of a number of beaten tracks in certain lines of the cerebral substance. Now, the presumption is that, as regards the claim for nourishment, this is the most costly of all the processes 'of the intelligence. To exercise a power once acquired should be a far easier thing, much less expensive, than to build up a new acquirement. We may be in sufficiently good condition for the one, while wholly out of condition for the other. Indeed, success in acquirement, looking at it from the physiological probabilities, should be the work of rare, choice, and happy moments; times when cerebral vigor is both abundant and well-directed.