great amount of energy which may be expended in thought and emotion, or which may issue directly in movement. Every one knows 
Diagram B, from Starr, Atlas of Nerve Cells, page 39, modified especially to show nucleus which is depleted of energy when the cell is in action. that a mere whisper of the death of a dear friend or of an approaching calamity or any similar circumstance will create great mental disturbance and drain the nerve cells to the point of exhaustion. So the prick of a pin or a tickling of the sole of the foot will produce vigorous movements of the entire body in most persons. It is probably true that in almost all instances the physical or mental resultant of a given stimulus is far greater, from the point of view of energy expended, than the stimulus itself. Every stimulus entering the cerebral cells is re-enforced from the energy stored therein; and it is plain, of course, that the less the supply or the greater the demands made the more rapidly will exhaustion follow. In a study, then, of brain fatigue in childhood we have to consider first the conditions which determine the amount of energy which shall be stored in the cells, which, as we shall attempt to show, differs in individual cases on account of a variety of varying circumstances; and, secondly, we have to regard the character of the work done, so as to notice how heavily it draws upon the credit of the brain.
It is the purpose here to consider especially the intellectual and emotional concomitants of brain fatigue in childhood. In 
Diagram C.—S = stimuli pouring into the brain (E) through all the senses, and issuing in mental action or movement (M). It shows that the energies of the brain are being drawn upon continually to re-enforce the stimuli from the outer world. order to ascertain these we may employ any or all of several methods of inquiry. In the first place, we may make direct mental tests to determine if a child can think as rapidly and logically in a state of fatigue, occasioned by overwork or by lack of food, as when refreshed after rest or proper nutrition. In the second place, we may by introspection observe the effects of fatigue upon our own processes of thinking and the character and quality of our feelings. Third, we may study children in their everyday work and play, and observe the influence upon their thinking and feeling of prolonged periods of activity, of great excitement or overstimulation of any sort, of a lack of proper and sufficient food, and other like conditions. Again, we may by observation, and by experiment with apparatus,
