11. Enumerate conditions in the schoolroom that dissipate the nervous energy of pupils; that economize it. CHAPTER XX - PRODUCTION OF SENSATIONS Our study of the nervous system has shown that impulses arising at the surface of the body are able, through connecting neurons, to bring about various activities. Moving along definite pathways, they induce motion in the muscles, and in the glands the secretion of liquids. It is now our purpose to consider the effect produced by afferent impulses upon the brain and, through the brain, upon the mind.(114) This effect is manifested in a variety of similar forms, known as *The Sensations.*—Sensations constitute the lowest forms of mental activity. Roughly speaking, they are the states of mind experienced as the _direct_ result of impulses reaching the brain. In a sense, just as impulses passing to the muscles cause motion, impulses passing to the brain cause sensations. The feeling which results from the hand’s touching a table is a sensation and so also is the pain which is caused by an injury to the body. The mental action in each case is due to impulses passing to the brain. Care must be exercised by the beginner, however, not to confuse sensations with the nervous impulses, on the one hand, or with _secondary_ mental effects, such as emotion or imagination, on the other. Sensations are properly regarded as the first conscious effects of the afferent impulses and as the _beginning stage_ in the series of mental processes that may take place on account of them. In some way, not understood, the mind associates the sensation with the part of the body from which the impulses come. Pain, for example, is not felt at the brain where the sensation is produced, but at the place where the injury occurs. This association, by the mind, of the sensations with different parts of the body, is known as "localizing the sensation." *Sensation Stimuli.*—While the sensations are dependent upon the afferent impulses, the afferent impulses are in turn dependent upon causes outside of the nervous system. If these are removed, the sensations cease and they do not start up again unless the exciting influences are again applied. Any agency, such as heat or pressure, which, by acting on the neurons of the body, is able to produce a sensation, may be called a _sensation stimulus_. It has perhaps already been observed that the stimuli that lead to voluntary action, as well as those that produce reflex action of the muscles, cause sensations at the same time. From this we may conclude that sensation stimuli are the same in character as those that excite motion. On the other hand, it should be noted that sensations are constantly resulting from stimuli that are of too mild a nature to cause motion.