The size of the red corpuscles is diminished by carbonic acid, by morphine, or by warmth, either applied locally on the hot stage of a microscope, or acting on them in the vessels of an animal suffering from fever.

It is increased by oxygen, hydrocyanic acid, quinine, or cold; and an increase occurs also in cases of anaemia.1

The red corpuscles pass out of the capillaries like the white, but they do so very slowly indeed, and in small numbers, under ordinary circumstances. Excess of sodium chloride in the blood causes them to pass out much more quickly;2 and rattle-snake poison, when locally applied, produces such sudden extravasation that it is impossible to follow the process: the whole field of the microscope becoming suddenly covered with blood.3