THE PREVENTION OF INFECTIOUS DISEASE. 415 



that the intentional modification of these con- 

 ditions of life may affect the predisposition 

 toward disease. The microbes that are present 

 in any given locality may be able, as already 

 pointed ont, to act in such a way as either to 

 heighten or diminish the predisposition to dis- 

 ease, so that in this respect also the influence 

 exerted upon the body may possibly be, and in 

 individual cases can even be demonstrated to 

 be, a particular example of the action of exter- 

 nal conditions. 



Along this line of hygienic education, in ad- 

 dition to a comprehensive supervision of bodily 

 welfare in the schools through gymnastics, 

 athletic sports and games, the controlling 

 authorities should see to the creation and ad- 

 vancement of a system of instruction in scien- 

 tific and practical hygiene adapted to the capac- 

 ity of the schoolchildren. There should be, in 

 connection with the instruction in natural his- 

 tory and natural science, instruction in hygiene 

 planned respectively for the common schools, 

 the secondary schools and the professional 

 schools. Starting from the structure and 

 mechanism of the human body and the pre- 

 sentation of its daily needs it is possible to ar- 

 rive at some understanding of the general con- 

 ditions of life and so advance from personal 

 hygiene to public hygiene. Along this same 



