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MICROBES, FERMENTS, AND MOULDS, 
CHAPTER V. 
THE MICROBES OF HUMAN DISEASES, 
I. Microses or Arr, EARTH, AND WATER. 
It is generally admitted that the large majority of 
epidemic and contagious diseases which affect men 
and animals are caused by the. introduction of certain 
kinds of microbes into the organism.. In reply to the 
question how these microbes are introduced into the 
body, and where they are before entering it, it is easy 
to show that these microbes exist in immense numbers 
—they or their spores—in the air we breathe, in the 
water we drink, in the ground on which we tread, 
and whence there rises, whenever it is dry, a fine dust 
charged with all sorts of germs, which penetrate 
together with the air into our mouths and lungs. 
For a long while we were almost completely 
ignorant of the conditions of existence of these 
microbes when they are in the soil or water. The 
recent researches of Zopf, a German botanist, tend to 
show that among the inferior algze termed Bacteria 
