he stomach, yet it is indebted to that viscus for its
continuance."(5)

THE FUNCTION OF RESPIRATION

It is a curious commentary on the crude notions of mechanics of previous
generations that it should have been necessary to prove by experiment
that the thin, almost membranous stomach of a mammal has not the power
to pulverize, by mere attrition, the foods that are taken into it.
However, the proof was now for the first time forthcoming, and the
question of the general character of the function of digestion was
forever set at rest. Almost simultaneously with this great advance,
corresponding progress was made in an allied field: the mysteries of
respiration were at last cleared up, thanks to the new knowledge of
chemistry. The solution of the problem followed almost as a matter
of course upon the advances of that science in the latter part of the
century. Hitherto no one since Mayow, of the previous century, whose
flash of insight had been strangely overlooked and forgotten, had even
vaguely surmised the true function of the lungs. The great Boerhaave
had supposed that respiration is chiefly important as an aid to the
circulation of the blood; his great pupil, Haller, had believed to the
day of his death in 1777 that the main purpose of the function is to
form the voice. No genius could hope to fathom the mystery of the lungs
so long as air was supposed to be a simple element, serving a mere
mechanical purpose in the economy of the earth.

But the discovery of oxygen gave the clew, and very soon all the
chemists were testing the air that came from the lungs--Dr. Priestley,
as usual, being in the van. His initial experiments were made in
1777, and from the outset the problem was as good as solved. Other
experimenters confirmed his results in all their essentials--notably
Scheele and Lavoisier and Spallanzani and Davy. It was clearly
established that there is chemical action in the contact of the air with
the tissue of the lungs; that some of the oxygen of the air disappears,
and that carbonic-acid gas is added to the inspired air. It was shown,
too, that the blood, having come in contact with the air, is changed
from black to red in color. These essentials were not in dispute from
the first. But as to just what chemical changes caused these results
was the subject of controversy. Whether, for example, oxygen is actually
absorbed into the blood, or whether it merely unites with carbon given
off from the blood, was lon