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细胞与温度
Cells
cannot
remain
alive
outside
certain
limits
of
temperature
and
much
narrower
limits
mark
the
boundaries
of
effective
functioning.
细胞只能在一定的温度范围内存活，而进一步保证它们有效工作的温度范围就更小了。
Enzyme
systems
of
mammals
and
birds
are
most
efficient
only
within
a
narrow
range
around
37
C;
a
departure
of
a
few
degrees
from
this
value
seriously
impairs
their
functioning.
哺乳动物和鸟类的酶系统只能在37℃左右的很小范围内才能有效工作。与此相差仅几度的温度都会大大削弱它们的工作效率。
Even
though
cells
can
survive
wider
fluctuations
the
integrated
actions
of
bodily
systems
are
impaired.
尽管温度变化更大时细胞仍能存活，但机体系统的整体运行能力却被削弱了。
Other
animals
have
a
wider
tolerance
for
changes
of
bodily
temperature.
其它动物对体温的变化有更强的适应性。
For
centuries
it
has
been
recognized
that
mammals
and
birds
differ
from
other
animals
in
the
way
they
regulate
body
temperature.
几个世纪以来，人们就认识到哺乳动物和鸟类调节体温的方式与其它动物不同。
Ways
of
characterizing
the
difference
have
become
more
accurate
and
meaningful
over
time,
随着时间的推移，人们对这种差异的描述越来越精确和有意义，
but
popular
terminology
still
reflects
the
old
division
into
"
warm-
blooded"
and
"
cold-
blooded"
species;
但是"暖血动物"和"冷血动物"这一古老的分类方式至今仍在大众词汇中有所反映。
warm-
blooded
included
mammals
and
birds
whereas
all
other
creatures
were
considered
cold-
blooded.
暖血动物包括哺乳动物和鸟类，其它动物统统被视为冷血动物。
As
more
species
were
studied,
it
became
evident
that
this
classification
was
inadequate.
但是对更多物种进行的研究表明这种分类显然是不适当的。
A
fence
lizard
or
a
desert
iguana-
each
cold-
blooded----
usually
has
a
body
temperature
only
a
degree
or
two
below
that
of
humans
and
so
is
not
cold.
美洲一种小型蜥蜴和沙漠鬣蜥同属冷血动物，但实际上它们的体温通常只比人类的体温低1～2度，因此并不是真正的冷血。
Therefore
the
next
distinction
was
made
between
animals
that
maintain
a
constant
body
temperature,
called
home0
therms,
因此又出现了恒温动物(即保持恒定体温的动物)
and
those
whose
body
temperature
varies
with
their
environments,
called
poikilotherms.
和变温动物(即体温随外界环境的变化而改变的动物)这一区分方式。
But
this
classification
also
proved
inadequate,
because
among
mammals
there
are
many
that
vary
their
body
temperatures
during
hibernation.
但这种分类也不恰当。因为有不少哺乳动物在冬眠期间会改变体温，
Furthermore,
many
invertebrates
that
live
in
the
depths
of
the
ocean
never
experience
change
in
the
depths
of
the
ocean
never
experience
change
in
the
chill
of
the
deep
water,
而许多生活在深海的无脊椎动物在寒冷的深海水域中体温并不变化，
and
their
body
temperatures
remain
constant.
而是恒定的。
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