2. The cells of the hemispheres of the brain contain a considerably larger amount of water during the younger periods of life than they do during the adult period. One of the results of this condition of the brain is that of less stability of character, and a larger measure of susceptibility. It is more sensitive and easily disturbed by external surroundings, while the influences which act upon it, in connection with its daily experiences, tend to create a much more rapid metamorphosis of its tissues. The nerve tissue of the brain in adult life is the most unstable in its elemental composition of that of any organ, but in childhood and youth the change resulting in degeneration and restoration of tissue is much more rapid than at any other period. Hence the importance of frequent and considerably long-continued periods of sleep and inactivity of this organ. Now, my observation and experience lead me to believe that young children in our cities sleep far too little to enable the brain to receive the largest benefit from it; that they are out on the streets, or employed at tasks, long after they should have been in bed. In many portions of our large cities there exist excitement and noise, which are quite sufficient to prevent sleep, until the system is very greatly fatigued, and the nervous elements exhausted. Parents are frequently thoughtless and careless in this respect, and the children are left out on the street or visiting at neighbors' houses until too late an hour. A teacher in a public school informs me that one of the greatest hindrances in the advancement of some of her scholars, lies in the fact that one or two nights of every week these children are out at musical or dancing parties, or attending some place of public amusement, so that the period of sleep is greatly abridged, and the brain has not recuperated its energy so as to be able to study. The sensitive tissue is in a condition of too great weakness to be much used, and in consequence the difficulty of learning lessons is greatly increased. Again, children are often called in the morning, long before enough sleep has been secured to refresh the brain, and employed in different ways, perhaps in attending to some piece of machinery in a large factory, which is filled with dust and the noise of thousands of wheels, and kept there ten or twelve hours a day; and the brain is not allowed to sleep for sixteen or seventeen hours. Now, one of the effects of these long periods of wakefulness and over-activity is to check the normal development of the brain, to stint its growth, and give it a twist from which it never recovers. This habit, formed in childhood, frequently extends into adult life, and becomes so fixed that it is difficult for the brain afterward to change its custom. The period of wakefulness tends to increase so that sleep is limited to six or seven instead of eight or nine hours.