3 i2 THE POPULAR SCIENCE MONTHLY. 



In our search for means of preventing disease we have been 

 led, as we see, beyond the province of medicine and into that of 

 education. But the connection between these two fields, from 

 our standpoint, extends much further, as we shall find. Though 

 muscular exercise be carried to the point of perfection, and the 

 surrounding conditions leave nothing to be desired, health is not 

 assured ; for, should the expenditure of energy be too great, there 

 will still be marked interference with development. Hence, the 

 expenditure as well as the development of energy must be con- 

 sidered. 



Now, the energy is expended by the organs in the performance 

 of their functions. Though ultimately derived from the food, its 

 proximate source is, at least in great part, the tissues, which, by 

 undergoing combustion, furnish the required energy ; whether it 

 be all derived in this way, or whether it be in part supplied im- 

 mediately by the blood, is a matter which has no influence upon 

 our problem. It is essential, however, to bear in mind that the 

 amount of energy which can be developed in a given space of time 

 is limited to the quantity of food digestible during this period, 

 and, if it be expended more rapidly tha n it is thus supplied, the func- 

 tions are performed at the expense of the tissues. If, therefore, 

 we desire to guard the system against waste and allow the organs 

 to develop properly, we must, as far as possible, limit functional 

 activity. There are, however, only two functions over which we 

 can exert a direct voluntary influence, namely, the muscular and 

 the mental. But as there is ample compensation for the energy 

 expended in muscular activity while there is none, in the physical 

 sense, for that used in mental action, it is clear that if we desire to 

 economize we must do so by exercising control over mental labor. 

 That the energy expended by the brain during its activity is de- 

 rived from the same source as that required for the performance 

 of the other functions is, to-day, a generally accepted fact. 



But, in order that it may not interfere with physical develop- 

 ment, mental labor must be regulated both quantitatively and 

 qualitatively. 



In regard to quantity, the number of school hours must not be 

 excessive ; and introduction into school life should be gradual, so 

 that the labor may be in proportion to the age and strength of the 

 child. In Germany this rule is observed, the children beginning 

 with about sixteen hours per week, to which two are added every 

 year until the fifth or sixth, when the maximum is reached. 

 The amount of work required at school, and in the preparation of 

 lessons, likewise needs careful consideration. 



From the qualitative standpoint the methods of instruction 

 play an important part. When the laws of psychology are ob- 

 served, the mind being treated in accordance with its nature, the 



