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0 3 0 8 托 福 试 题
阅读( 55minutes )
Question 1-11
If food is allowed to stand for some time, it
putrefies .When the putrefied material
is examined microscopically ,it is found to be teeming
with bacteria. Where do these
bacteria come from , since they are not seen in fresh
food? Even until the mid-nineteenth
century, many people believed that such microorganisms
originated by spontaneous
(5 ) generation ,a hypothetical process by which living
organisms develop from nonliving
matter.
The most powerful opponent of the theory of
spontaneous generation was the French chemist and
microbiologist Louis Pasteur(1822-1895).Pasteur showed
that structures
present in air closely resemble the microorganisms seen
in putrefying materials .He did
(10) this by passing air through guncotton filters, the
fibers of which stop solid particles. After
the guncotton was dissolved in a mixture of alcohol and
ether, the particles that it had
trapped fell to the bottom of the liquid and were
examined on a microscope slide .Pasteur
found that in ordinary air these exists a variety of
solid structures ranging in size from
0.01 mm to more than 1.0 mm .Many of these bodies
resembled the reproductive
(15) structures of common molds, single-celled animals, and
various other microbial cells .
As many as 20 to 30 of them were found in fifteen liters
of ordinary air ,and they could
not be distinguished from the organisms found in much
larger numbers in putrefying ma
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