ming this substance from other organic bodies, such, for
example, as starch. Plants elaborate fat directly from the
minerals--carbonic acid gas, and water.

I have already explained that the growth of plants is, _caeteris
paribus_, directly proportionate to the amount of sunlight to which
they are exposed. Not less certainly is the force which constitutes the
sun-beam expended in grouping mineral atoms into organic forms, than is
the heat which converts water into steam. But in neither case is the
force destroyed. When the vaporous steam is condensed into the liquid
water, all the heat is restored, and becomes palpable. By the ultimate
decomposition of vegetable substances all the force expended on their
production is liberated, and, in some form, becomes manifest.

When the fat formed in the mechanisms of plants is decomposed in
the animal organism, two results follow:--The atoms of the fat are
re-converted to their original mineral, or statical conditions of
carbonic acid gas and water; and the force which maintained them in
their organic state is set free as heat, and its equivalent, motive
power.

One of the most useful instruments which the ingenuity of man has
devised, is the Thermometer. It is so familiarly known that I need
not describe it. This instrument does not enable us to estimate the
actual quantity of heat contained in a substance, but it indicates
the proportion of that subtile element which is _sensible_--that is
recognisable by the sense of touch. The dusky Hindu, clad in his single
cotton garment, and the Laplander in his suit of fur, are placed under
the most opposite conditions in relation to the heat of the sun--the
Indian is exposed during the whole year to Sol's most ardent beams,
whilst but a scant share of its genial rays goes to warm the body of
the Laplander. Now, if we placed the bulb of a thermometer beneath the
tongue of a Hindu, we would find the mercury to stand at 98 degrees on
Fahrenheit's scale, and if we repeated the experiment on a Laplander,
we would obtain an identical result. Numerous experiments of this
nature have been made on individuals in most parts of the world, and
the results have proved that the temperature of the blood of man is
98 degrees Fahrenheit, whether he be in India or at Nova Zembla, on
the _steppes_ of Russia, or the elevated _plateaus_ of America. This
invariability[6] of the temperature of the bodies of men and of all
other warm-blooded animals, appears