*Physical Exercise* properly taken is beneficial to the nervous system through both direct and indirect effects. A large proportion of the nerve cells have for their function the production of motion, and these are called into play only through muscular activity. Then, as already suggested, physical exercise counteracts the unpleasant effects of mental work. Hard study causes an excess of blood to be sent to the brain and a diminished amount to the arms and to the legs. Physical exercise redistributes the blood and equalizes the circulation. Light exercise should, therefore, follow hard study. The student before retiring at night is greatly aided in getting to sleep and is put in a better condition for the next day’s work by ten to fifteen minutes of light gymnastics. A daily walk of two or three miles is also an excellent means of counteracting the effects of mental work. The brain worker should, however, avoid violent exercise or the carrying of any kind of exercise to exhaustion. *Sleep*, and plenty of it, is one of the first requirements of the nervous system. It is during sleep that the exhausted brain cells are replenished. To shorten the time for sleep is to weaken the brain and to lessen its working force. No one should attempt to get along with less than eight hours of sleep each day and most people require more. Children require more sleep than adults. Those under six years should have from eleven to twelve hours of sleep per day. Children between six and ten years should have at least ten hours. *Insomnia*, or sleeplessness, on account of its effects upon the nervous system, is to be regarded as a serious condition, and hygienic means for relieving it should be diligently sought. Having its cause in nervousness, a disturbed circulation of the brain, or some form of nervous exhaustion, it is benefited through relieving these conditions and in the manner already described. Of course the external conditions for aiding sleep should not be overlooked. The bed should be comfortable, and the room should be cool, well ventilated, dark, and quiet. The inducing of sleep by means of drugs is a dangerous practice and should never be resorted to except under the direction of the physician. *Effects of Heat and Cold.*—Heat and cold both have their effects upon the nervous system. Heat increases the nervous irritability, while cold acts as a natural sedative to the nerves. A nervous person is made more nervous by an overheated atmosphere, but derives beneficial effects from exposing the body freely to cold air and water. The tonic cold bath (page 273), if taken with the usual precautions, can be used to good advantage in diminishing nervousness. The taking of outdoor exercise in cold weather is, for the same reason, an excellent practice.