PHYSICAL VIGOR A PROTECTION 251 



of increasing the physical vigor of its members. This can 

 be done by wholesome food, by exercise, and by fresh air. 

 An active body is far less liable to disease than one more 

 or less passive, and vigorous exercise in the open air, 

 accompanied by plenty of wholesome but not too rich 

 food, will be the most thorough safeguard an individual 

 can have against the attack of some infectious diseases, 

 especially tuberculosis. The need of fresh air should be 

 emphasized, perhaps, more than any other point, for the 

 air in houses, for reasons already indicated, is much more 

 liable to be filled with infectious material than the out- 

 door air, and a person who constantly remains in the 

 house is much more liable to yield to contagion. If, 

 however, he is careful to exercise in the open air, he will 

 ward off attacks to which otherwise he might yield. 

 This applies even more forcibly to the air of our sleeping 

 rooms than to that of our living rooms, for fresh air in 

 the sleeping room is one of the greatest desiderata in 

 maintaining good health. The belief that night air is 

 injurious is responsible for much ill health. Sleeping in 

 close rooms without sufficient air causes a general lower- 

 ing of bodily vigor. Our sleeping rooms should have 

 the windows open even in cold weather, and, provided 

 there be mosquito nettings at the windows to keep out 

 insects, there is absolutely nothing to be feared in night 

 air. While vigorous health is a protection against some 

 diseases (tuberculosis), it is far less efficient against others 

 (smallpox). 



It should always be borne in mind that contagious 

 diseases are real things, and not the result of imagination. 

 They are produced in our bodies by the growth of certain 



