With the increase of mental activity alluded to, there have come into a fuller range of activity those portions of the brain which are concerned with thought, and which, in the narrow limits and simple conditions before experienced, had been comparatively inactive. Consequently, a larger supply of blood has been summoned to these parts of the brain to repair the loss incurred by this increased activity. This change and consequent disturbance in the relative blood-supply, as between the brain and other parts of the system, would be of little importance if sufficient care be exercised that it comes in the right degree, and does not cause too great activity in the organ of the mind; indeed, there might be expected favorable results from a larger exercise of function, or at least not unfavorable ones. In the experience of modern times, however, this has not proved to be the case. With the measure of mental power and scope which attends the change, there has been a large tendency to over-stimulate the intellectual faculties, which has been aided and thought to be necessary, in consequence of the immense competitions and business activities of modern civilization. This tendency to stimulation has been manifest even to a much larger extent than formerly, first, in the matter of education. The new conditions and employments of life, rendered prominent by some of the discoveries which pertain to science, agriculture, commerce, and the general conduct of business pursuits, have developed requirements on the part of those who are called upon to conduct them, which have been heretofore unknown. To meet these requirements it has been thought necessary to pursue such courses of education, and to present such special incentives to study on the part of the young, by the use of prizes and grades of scholarship, and public exhibitions, as will bring into operation the largest possible activity, and secure the highest discipline of the brain, even at a very early period of life. At this time all the forces of vitality and physical growth are in the fullest activity, so that the strain comes upon the brain at the period when it has the least of ability to bear it, and at expense to other portions of the system. And again, in the use of stimulants, especially alcohol, in some of its forms, and tobacco, during the period of growth and early manhood. The use of these substances, as well as the subject of education, in their effects upon the nervous system, will be discussed more fully in future chapters, and are only mentioned, in this connection, as causes of nerve degeneration, which have come into operation more fully through the influence of modern civilization.