It should go almost without saying that to get the _best_ effects from
air you should breathe the purest air obtainable.
Air which is full of dust particles, for instance, may be actually
irritating to the delicate mucous membrane that lines the nose, throat,
bronchial tubes and air cells of the lungs.
This dust contains particles of organic matter derived from the
excrement of horses and dogs, from dried atoms of offal and decaying
vegetable matter, or from dried mud impregnated with urine.
Indeed, it is very largely upon these particles that the
micro-organisms--arch enemies of mankind as well as of animal kind--are
carried on their errand of destruction.
These micro-organisms are most abundant in the air of inhabited
rooms--and the more people in the room the greater the number of
microbes present.
So don’t be afraid of open windows--day or night. Remember Florence
Nightingale’s quaint observation, “Windows are made to be opened.”