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DESCRIPTION OF THE SILK-WORM. 113
by any superadditions of heat. In both of these experiments
the quantity of food consumed, was as great as is usually given
during the longer period employed in the common manner of
rearing. After the second moulting had taken place in the
last experiment, the temperature was lowered to 82*^ ;
and it is
remarkable that the worms occupied only five days in comple-
ting their thud and fourth changes, although others which had
been accustomed to this lower degree from their birth occupied
seven or eight days for each of these moultings. It would there-
fore seem that the constitution of the insects can be affected,
and an impetus given to their functions at the period of their
first animation, which accompanies them through their after
stages. So far from this forcing system proving injurious to the
health of silk-worms, M. de Sauvagues found that his broods
were unusually healthy ; and that while the labors of cultiva-
tion were abridged in their duration, much of the attendant
anxiety was removed.
Like other caterpillars, the silk-worm is not a warm-blooded
animal, and its temperature is therefore always equal to that of
the atmosphere in which it is placed. In the silk-producing
countries, where modes of artificial heating have not been
studied practically and scientifically, the difficulty and expense
that must attend the prosecution of this heating system, form
abmidant reasons why it cannot be generally adopted. The
great susceptibility of the insect to atmospheric influences
would also in a great degree render unsuitable the more common
arrangements for the purpose. The plan of warming
apartments by means of stoves, in its passage through which
the air becomes highly heated before it mixes with and raises
the general temperature of the air in the chamber, is liable to
this inconvenience,—that the portion so introduced, having its
vital property impaired by the burning heat through which it
has passed, injures, proportionably, the respirable quality of the
whole atmosphere ; an effect which is easily perceptible by
those who inhale it. A better plan of heating has lately been
suggested, and is rapidly coming into practice, viz., of warming
buildings by a current of hot water (an American invention),
which is, by a very simple process, kept constantly flowing in
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