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13.

[[strikethrough]] about noon.  It is also a fact, established by experiment, that the more rapid the current, the more bacteria will it carry with it, although comparatively slow currents are required to move bacteria.  It is, therefore, clear that there must be a different reason why malarial infection takes place at a time of day when the difference of temperature may be such as to reverse the current. ^[[-]]

^[[b]] This peculiar circumstance is explained in the following way: It is considered that from moist soils---malaria most frequently occurs in such soils--during the heat of the day currents of moisture as well as air pass in a direction from the surface of the soil toward the upper warmer stratum of the atmosphere.  The germs of malarial infection, of course, are carried along ^[[,]] but[[strikethrough]],[[/strikethrough]] rapid diffusion takes place, preventing them from concentrating on any particular spot.  After sundown, the atmosphere rapidly cools and this fact causes the moisture to return to the soil in a condensed state or in the form of dew, carrying with it the germs 
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