complicated matters and delayed a complete understanding of the
chemical processes of respiration. It was some time, too, before
the idea gained acceptance that the most important chemical
changes do not occur in the lungs themselves, but in the ultimate
tissues. Indeed, the matter was not clearly settled at the close
of the century. Nevertheless, the problem of respiration had
been solved in its essentials. Moreover, the vastly important
fact had been established that a process essentially identical
with respiration is necessary to the existence not only of all
creatures supplied with lungs, but to fishes, insects, and even
vegetables--in short, to every kind of living organism.


ERASMUS DARWIN AND VEGETABLE PHYSIOLOGY

Some interesting experiments regarding vegetable respiration were
made just at the close of the century by Erasmus Darwin, and
recorded in his Botanic Garden as a foot-note to the verse:

"While spread in air the leaves respiring play."


These notes are worth quoting at some length, as they give a
clear idea of the physiological doctrines of the time (1799),
while taking advance ground as to the specific matter in
question:


"There have been various opinions," Darwin says, "concerning the
use of the leaves of plants in the vegetable economy. Some have