ADDITIONS TO CHAP. V. 
OF THE SOURCE OF THE CARBON IN VEGETABLES AND 
ANIMALS BY WHICH THE CHANGES IN THE AIR ARE 
EFFECTED. 
622. IN treating of the immediate source of the car- 
bon in living vegetables and animals, and of the mode 
in which it was yielded by them to combine with the 
oxygen gas of the air, during the exercise of the re- 
spiratory function, we endeavoured to shew that its 
emission was connected with the exertion of a living 
action ; and that it was not simply abstracted from 
the plant and animal by the operation of any affinity 
subsisting between it and the oxygen with which it 
combined. We therefore necessarily concluded, thajt 
the carbon was an excretion from the living body, 
depending, like other excretions, on the motion of 
the circulating fluids ; and ceasing to be afforded, 
when those fluids ceased to move. Although this 
part of our Inquiry has appeared to attract the least 
attention, yet, to ourselves, it has always seemed 
x 2 
