(1) The red corpuscle content of the blood is a constantly varying quantity under physiological conditions.
(2) Certain new means have been found by which the red count may be rapidly and greatly increased.
(a) Lung emboli produced by the injection of corpuscles hardened with formaldehyde, of an inert powder as lycopodium, or of oil.
(b) Emotional stimuli, as fright and rage.
(3) The polycythaemia produced by the injection of epinephrin is due to the action of the liver alone.
(4) Ligature of the arterial blood supply to the liver excludes the production of polycythaemia after the injection of epinephrin.
(5) Later release of this ligature allows the customary increase in number of red cells to take place, without the further injection of epinephrin.
(6) The liver effects this increase in number of red cells by
(a) A decrease in plasma volume, not sufficient to account for the entire increase in the number of red cells however.
(b) By bringing into the circulation red cells which were not present before the production of polycythaemia as shown by
(α) Their reduced size.
(β) Their reduced percentage haemoglobin content.
(7) These cells give none of the usual reactions of young cells. There is an absence of nucleated red cells, no change in the fragility of the corpuscles, and no increased metabolism of the red cells themselves, as shown by an increased rate of reduction.
(8) It is concluded that there is a mechanism for the regulation of the red corpuscles content of the blood.
(9) That the regulatory mechanism is under nervous control, reacting to lack of oxygen as a stimulus.
(10) That the adrenal glands play a part in this mechanism.
(11) That the liver is the organ which supplies the body with red cells to meet its acute demands.