33 2 THE POPULAR SCIENCE MONTHLY. 



by exercise, and all are nourished by the circulating blood. Think of 

 the immense strain upon the bodily powers to keep the brain and nerv- 

 ous system properly nourished ! It is calculated that the brain alone 

 requires one fifth of the entire supply of blood in the body. The 

 drain upon the bodily vigor of a brain-worker would be greater than 

 this fraction represents, if it were not for the law of Treviranus, ac- 

 cording to which an organ not only takes from the blood certain ma- 

 terials, but also supplies to it other materials. " Just as, on a larger 

 scale, the carbonic acid exhaled by animals is taken up by vegetables, 

 and a poison thus removed from the atmosphere in which the animal 

 lives, so by one organic element of the body the blood is purified from 

 the waste matter of a higher element, which would be poisonous to 

 it." * So that a tired brain and quivering nerves may not be more 

 wearied by physical exercise, but may be refreshed by it. This 

 refreshment may result from two processes : first, by withdrawing the 

 excessive supply of blood from the before active organ ; and, secondly, 

 by purifying the blood so that it may be ready to properly nourish 

 the brain. And the muscular system not only acts as a store-house of 

 vitality for the brain, and a purifier of its supply of blood, but it 

 covers the nervous system, acting as its stay and protection. " To be 

 weak is to be miserable. . . . Susceptibility of nerve and feebleness of 

 muscle generally go together." To correct one deficiency is usually to 

 cure the other weakness. 



To the young, physical exercise is essential to growth, both of body 

 and mind. Youth is not only the time to cultivate good habits, but 

 also the time to store up vitality. At that time many abnormal devel- 

 opments can be corrected by appropriate exercises. At that period, too, 

 the healthy balance between brain and body can better be established. 

 To children, exercise is specially needful for healthy nerves, since, as 

 compared with the nervous system of an adult, the nervous system of 

 a child is five times as large, in proportion to the size of the body. 

 In them, therefore, "that parasite of the blood," the brain, demands 

 that a greater amount of time should be given to waste and repair of 

 tissue by means of exercise, and that a greater amount of proper food 

 should furnish the supply of nourishment. Short intervals of study, 

 long intervals of play or light work of body, and that in the open air, 

 if possible, should be the rule for children. As they increase in years 

 more time can be given to conscious cerebration. At some periods of 

 growth, all the way from the age of twelve to eighteen, according to 

 the individual, special watchfulness is required of parents and instruct- 

 ors to see that the functions of growing organs are not interfered with 

 by excessive attention to brain-work. At this critical time no study 

 would be safer than too much study. 



After a good muscular system has been developed in childhood and 

 youth, a comparatively small amount of time judiciously devoted to 



* Maudsley. 



