1. Very small amounts of quinin can be recovered from defibrinated blood almost quantitatively (less perfectly from separated corpuscles) by shaking with chloroform, and such small amounts can be recovered equally well by dissolving the blood and tissues in sodium hydrate solution and extracting with chloroform.
2. Quinin can be determined quantitatively in extracts of tissues containing 0.5 mgm. of the base by titrating with bromin water.
3. When quinin is added to citrated whole blood of the cat and this is allowed to stand an hour, the corpuscles may retain the quinin in twice the concentration that it is present in the plasma but, on the other hand, under practically similar conditions the concentration in the plasma may equal that in the corpuscles. This is in harmony with various observations that quinin is fixed in the corpuscles in greater concentration than in the plasma under certain artificial conditions, and part of that so fixed is not removed by washing with normal salt solution.
4. About 95 per cent of an intravenous dose of quinin leaves the blood in the cat and dog within five minutes, and the greater part of this in two minutes, but the rate of disappearance from the circulation varies somewhat under conditions that are not known. Traces may be present in the blood of the dog after more than fifteen hours.
5. Quinin injected intravenously in the cat is rapidly fixed by the capillaries, from which as much as one-fourth of the total dose may be recovered by perfusion if the animal is exsanguinated within a few minutes. It seems probable that fixation by the capillaries is of importance in the destruction of the protozoa of malaria when quinin is used therapeutically.
6. The lungs, liver, heart. kidneys and brain contain quinin in higher concentration than the muscles or blood during the first two hours following intravenous injection in the dog and cat, but the relative and actual concentration in those organs changes constantly, and after three hours only about 1 per cent of the total dose can be recovered from these organs. This is due partly to destruction, as we shall show in a subsequent paper.