Note 19 — Chapter VIII
Reading edition
This statement does not hold in regard to Entozoa (animals living in the bodies of others), or at all events is not proved.
[20] The test for carbonic acid.
[21] A test for the presence of oxygen.
[22] It is in this paper that he uses the significant expression "ventilating the blood," which looks as if the refrigerating effect of respiration—and which we have endeavoured to show is the real, though perhaps not sole, purpose of it—had not wholly escaped his notice.