WHERE BACTERIA ARE FOUND.

There are no other plants or animals so universally found in
Nature as the bacteria. It is this universal presence, together
with their great powers of multiplication, which renders them of
so much importance in Nature. They exist almost everywhere on the
surface of the earth. They are in the soil, especially at its
surface. They do not extend to very great depths of soil, however,
few existing below four feet of soil. At the surface they are very
abundant, especially if the soil is moist and full of organic
material. The number may range from a few hundred to one hundred
millions per gramme. [Footnote: One gramme is fifteen grains.] The
soil bacteria vary also in species, some two-score different
species having been described as common in soil. They are in all
bodies of water, both at the surface and below it. They are found
at considerable depths in the ocean. All bodies of fresh water
contain them, and all sediments in such bodies of water are filled
with bacteria. They are in streams of running water in even
greater quantity than in standing water. This is simply because
running streams are being constantly supplied with water which has
been washing the surface of the country and thus carrying off all
surface accumulations. Lakes or reservoirs, however, by standing
quiet allow the bacteria to settle to the bottom, and the water
thus gets somewhat purified. They are in the air, especially in
regions of habitation. Their numbers are greatest near the surface
of the ground, and decrease in the upper strata of air. Anything
which tends to raise dust increases the number of bacteria in the
air greatly, and the dust and emanations from the clothes of
people crowded in a close room fill the air with bacteria in very
great numbers. They are found in excessive abundance in every bit