given out to surrounding bodies.

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The objection? 559. In what do all the physiologists of the present
day concur? How is it proved that respiration and animal heat are
closely connected? 560. What is said of the apparent heat of bodies?
How is this illustrated? 561. What is the effect when the density and
the arrangement of the atoms of a body are changed?

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_Illustrations._ 1st. Ice and salt, (Chl. of Sodium,) when mixed, are
converted into a fluid. In this state they will hold more heat than
when solid. The heat necessary to produce this change is drawn from
the surrounding medium, which is made proportionally colder by the
loss of caloric imparted to the ice and salt. It is by this chemical
process that "ice-cream" is made.

2d. On the other hand, mix water and sulphuric acid, (oil of vitriol,)
of the temperature of 60 deg., and the mixture will become quite warm,
and will freely impart its heat to surrounding and contiguous objects.

562. The same principle is exhibited, when oxygen unites with an
inflammable body, as in the burning of wood, coal, oil, &c. In
combustion, the oxygen of the atmosphere unites with carbon and
hydrogen, and carbonic acid and water are produced. This process,
according to all the known laws of caloric, is attended with heat. The
quantity of heat disengaged in combustion is always in proportion to
the amount of carbon and hydrogen consumed; thus a piece of wood
weighing one pound, in burning slowly, would give out the same
quantity of heat as a pound of shavings of the same wood, in burning
rapidly. Upon these principles, the production of animal heat may be
understood.

563. The food contains carbon and hydrogen. These exist in the chyle.
The old and waste atoms of the body likewise contain the same
elements. In the lungs the oxygen and nitrogen of the inspired air are
separated. It is now supposed that the oxygen enters the capillary
vessels of the lungs, and mingles with the blood, with which it is
carried to the heart and thence to the nutrient capillary vessels of
every part of the system.

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Give the 1st illustration. The 2d. 562. What changes take place when
oxygen unites with an inflammable body? To what is the quantity of
heat proportionate in combustion? Give an example. 563. How are carbon
and hydrogen supplied to the system? How the oxygen? Where does the
oxygen mingle with the blood?