THE MICROBES IN AIR AND WATER 29 
be alarming, were it not for the fact that most 
of these microbes are of the harmless kind. 
Yeasts and molds of all kinds are numerous. Are they 
The hay bacillus, another harmless type, is al- harmful 
most always present, along with many similar 
forms. As a rule, the microbes which cause 
disease are rare in dry dust. The germ of 
tuberculosis, for instance, may float in the air 
of a room in which a person sick with the dis¬ 
ease is living, but it lives only a comparatively 
short time and is not found in ordinary air. 
The air of the school-room may contain a few 
germs from children suffering from colds or 
other diseases, but if it has plenty of sunshine 
and fresh air, they rarely live long. The air is 
not a suitable place for microbes to live in and 
multiply, for it contains none of the foods they 
need. They are simply floating about waiting 
for a chance breeze to blow them to some spot 
favorable for their growth. If it does not, they 
soon die from lack of necessary food and mois¬ 
ture. So you see that dust is not nearly so 
harmful as many people once thought it was. 
