Page:Popular Science Monthly Volume 51.djvu/670

654 Dr. Stanley Hall has said somewhere that the time may not he far away when we can say that what is physiologically right is morally right—that is, whatever begets the best physiological conditions will produce the best moral character.

If brain fatigue interferes with the readiness and accuracy of one's intellectual operations and estranges the emotional nature, it is important to know what are the agencies most commonly found in home and school which produce this condition; for when the various qualities of which dullness and irritability are types are characteristic of one's childhood they tend to become permanent, thus determining one's character. It is shown by neurology that any mental act oft repeated leads to the establishment of correlated neural processes which make the reproduction of that act continuously easier until it becomes automatic, when all the causes which originally produced it even if with conscious effort on the part of the individual will in time awaken it without any such difficulty. If now it be remembered that brain fatigue is due to some degree of exhaustion of cerebral cells, it will be apparent that one of the most important sources of fatigue is inadequate nutrition of the brain. Nerve cells, like all other cells in the body, repair themselves by absorbing from the blood those materials suited to their particular needs. If the blood does not carry to them a sufficient quantity of the right elements of food to meet the demands made upon them, then while thus neglected they will be in a partially exhausted state from sheer inability to obtain nutriment. Just so a field of wheat in poor soil will bring forth imperfect grain, or a fruit tree unable to find the proper elements of nutrition will bear defective apples or pears or peaches.

All life of whatsoever kind requires a proper sort and adequate amount of nutrition in order that it may develop in a vigorous, healthy manner. Experiments have been conducted in rearing tadpoles and pond snails in various sized vessels of water, where the opportunities for nutrition corresponded with the quantities of water inclosed, and it has been found that the less the amount of water the smaller the animal. Animals reared in this way may be arranged in a series increasing in size according to the quantity of water in which they have been placed. Many mammals and birds are found to have their centers of distribution in the northern regions, and they diminish in size from the northern to the southern latitudes, thus indicating that the ability to obtain food determines the degree of development of the bird or