If food is allowed to stand for some time, it putrefies .When the putrefied material+ T9 X+ r$ x3 n: F, C* {
is examined microscopically ,it is found to be teeming with bacteria. Where do these 0 F+ Y4 g r6 h$ E! u s
bacteria come from , since they are not seen in fresh food? Even until the mid-nineteenth
! S# \+ `' P( N; z8 p6 Qcentury, many people believed that such microorganisms originated by spontaneous6 f7 K) ?/ b; F0 H
(5 ) generation ,a hypothetical process by which living organisms develop from nonliving
1 D! ]) ^6 e: o4 N4 Kmatter., m5 O& A! `/ {4 D% ^
The most powerful opponent of the theory of spontaneous generation was the French chemist and microbiologist Louis Pasteur(1822-1895).Pasteur showed that structures , n$ q5 ]& @+ q h
present in air closely resemble the microorganisms seen in putrefying materials .He did 8 s% o* G5 h& L4 T6 E; g% K
(10) this by passing air through guncotton filters, the fibers of which stop solid particles. After
/ s- a3 D- d9 `$ o% r# ~the guncotton was dissolved in a mixture of alcohol and ether, the particles that it had y" g* r7 k% I* j5 u3 J5 U: h
trapped fell to the bottom of the liquid and were examined on a microscope slide .Pasteur1 R( C5 a$ C+ o) P8 N
found that in ordinary air these exists a variety of solid structures ranging in size from ! ]2 Q- j6 H+ ^" U0 U, y, R
0.01 mm to more than 1.0 mm .Many of these bodies resembled the reproductive 1 u3 z; P5 }7 S# v* d4 Z
(15)structures of common molds, single-celled animals, and various other microbial cells .3 f) m' F+ \$ G; p: r( M/ o
As many as 20 to 30 of them were found in fifteen liters of ordinary air ,and they could# e, M/ f$ k9 M
not be distinguished from the organisms found in much larger numbers in putrefying materials .Pasteur concluded that the organisms found in putrefying materials originated
9 q6 [3 b; v& [% m8 z; u from the organized bodies present in the air .He postulated that these bodies are constantly0 n$ ]$ P$ g. V& M/ z4 O
(20)being deposited on all objects.
" S7 D/ W0 J$ m3 ]6 HPasteur showed that if a nutrient solution was sealed in a glass flask and heated to
; \) K" [ \' B1 d8 Z6 {boiling to destroy all the living organisms contaminating it, it never putrefied .The proponents of spontaneous generation declared that fresh air was necessary for * w+ _ E; h$ N" h
spontaneous generation and that the air inside the sealed flask was affected in some way
. G: g. h N0 y y; Z/ u4 W' a(25)by heating so that it would no longer support spontaneous generation. Pasteur constructed a swan-necked flask in which putrefying materials could he heated to boiling, but air+ A3 I. |7 i7 E
could reenter. The bends in the neck prevented microorganisms from getting in the flask.. Material sterilized in such a flask did not putrefy.
: d( h( N) ]4 g, U2 i$ i/ X% ?
8 T# S, ~8 X- }0 u- a1,What does the passage mainly discuss?
" x/ I0 q" a. K9 K4 w/ K(a)Pasteur’s influence on the development of the microscope.
: {! a3 D g! h! @& L(b)The origin of the theory of spontaneous generation .
; C/ D1 ?+ D) F |: O, l. @/ Y(c)The effects of pasteurization on food.& `( Q: o1 S4 A
(d)Pasteur’s argument against the theory of spontaneous generation .# K8 a+ m0 W! D1 S/ g& }% y
2,The phrase “teeming with ”in line 2 is closest in meaning to
+ d& F* I) ?8 D+ M& ]$ q(a)full of7 H1 I- Y; T; z, o$ i \
(b)developing into
% V- K+ }3 z' c(c)resistant to# c$ i" x" F2 `4 f. G
(d)hurt by |
发表于 2012-8-14 22:34:35
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