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 long in dispute.

Each of the main disputants was biased by his own particular
views as to the moot points of chemistry. Lavoisier, for
example, believed oxygen gas to be composed of a metal oxygen
combined with the alleged element heat; Dr. Priestley thought it
a compound of positive electricity and phlogiston; and Humphry
Davy, when he entered the lists a little later, supposed it to be
a compound of oxygen and light. Such mistaken notions naturally