gestive parts
especially; and alternately the portion which is so changed is carried
through our lungs by one set of vessels, while the air that we inhale and
exhale is drawn into and thrown out of the lungs by another set of
vessels, so that the air and the food come close together, separated only
by an exceedingly thin surface: the air can thus act upon the blood by
this process, producing precisely the same results in kind as we have seen
in the case of the candle. The candle combines with parts of the air,
forming carbonic acid, and evolves heat; so in the lungs there is this
curious, wonderful change taking place. The air entering, combines with
the carbon (not carbon in a free state, but, as in this case, placed ready
for action at the moment), and makes carbonic acid, and is so thrown out
into the atmosphere, and thus this singular result takes place: we may
thus look upon the food as fuel. Let me take that piece of sugar, which
will serve my purpose. It is a compound of carbon, hydrogen, and oxygen,
similar to a candle, as containing the same elements, though not in the
same proportion--the proportions being as shewn in this table:--

SUGAR.

Carbon, . . . . 72
_
Hydrogen, . . . 11 |
| 99
Oxygen, . . . . 88_|

This is, indeed, a very curious thing, which you can well remember, for
the oxygen and hydrogen are in exactly the proportions which form water,
so that sugar may be said to be compounded of 72 parts of carbon and 99
parts of water; and it is the carbon in the sugar that combines with the
oxygen carried in by the air in the process of respiration--so making us
like candles--producing these actions, warmth, and far more wonderful
results besides, for the sustenance of the system, by a most beautiful and
simple process. To make this still more striking, I will take a little
sugar; or, to hasten the experiment, I will use some syrup, which contains
about three-fourths of sugar and a little water. If I put a little oil of
vitriol on it, it takes away the water, and leaves the carbon in a black
mass. [The Lecturer mixed the two together.] You see how the carbon is
coming out, and before long we shall have a solid mass of charcoal, all of
which has come out of sugar. Sugar, as you know, is food, and here we have
absolutely a solid lump of carbon where you would not have expected it.
And if I make arrangements so as to oxidize the carbon of sugar, we shall
have a much mor