xiated persons?

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CHAPTER XXVII.

ANIMAL HEAT.

545. The true sources of animal heat, or calorification, are still
imperfectly known. No hypothesis has, as yet, received the concurrent
assent of physiologists. We see certain phenomena, but the ultimate
causes are hidden from our view. Its regular production, to a certain
degree, is essential both to animal and vegetable life.

546. There is a tendency between bodies of different temperature to an
equilibrium of heat. Thus, if we touch or approach a hot body, the
heat, or caloric passes from that body to our organs of feeling, and
gives the sensation of heat. On the contrary, when we touch a cold
body, the heat passes from the hand to that body, and causes a
sensation of cold.

547. The greater number of animals appear cold when we touch them;
and, indeed, the temperature of their bodies is not much above that of
the atmosphere, and changes with it. In man, and other animals that
approach him in their organization, it is otherwise. They have the
faculty of producing a sufficient quantity of caloric to maintain
their temperatures nearly at the same degree, under all atmospheric
changes, and keep themselves warm.

548. Those animals whose proper heat is not very perceivable, are
called _cold_-blooded; as most species of fishes, toads, snakes,
turtles, and reptiles generally. Those animals which produce
sufficient heat independently of the atmosphere surrounding them, are
called _warm_-blooded; as man, birds, quadrupeds, &c.

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545-570. _What is said respecting animal heat?_ 545. Are the true
sources of animal heat known? What do we see? 546. What is the tendency
between bodies of different temperatures? Give an explanation. 547.
What is said of the temperature of animals? 548. What is meant by
cold-blooded animals? By warm-blooded animals?

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549. The temperature of man is about 98 deg., (Fahrenheit's thermometer,)
and that of some other animals is higher; the temperature of birds,
for example, is about 110 deg. It is obvious, that in most parts of the
globe, the heat of the atmosphere is, even in summer, less than that
of the human body. In our latitude, the mercury rarely attains 98 deg.,
and sometimes it descends to several degrees below zero.

550. Captain Parry, with his ship's company, in his voyage of
discovery to the arctic regions, wintered in a climate where the