1. Doses of less than six milligrams of hematin and, under certain conditions, larger doses may cause a slight rise of blood pressure.

2. Large doses of hematin cause a profound and prolonged fall of blood pressure. The principal factor in this fall of blood pressure is the marked dilatation of the splanchnic vessels. The splanchnic dilatation either does not occur at all or but very slightly if the splanchnic nerves are cut. The splanchnic dilatation is partly compensated for by a marked constriction of cutaneous vessels and it seems probable that the cutaneous constriction is active and not simply passive to the splanchnic engorgement.

3. Hematin acts upon the cardio-inhibitory center causing a marked slowing of the rate of heart-beat, and in large doses produces a typical vagal pulse or even marked irregularities in the amplitude and rhythm of the pulse. Under hematin the heart at first shows great loss of tone but later the tone increases beyond the normal. The cardiac output for a time is greatly diminished.

4. In the large doses employed by us, hematin depresses the respiratory center and death under hematin is due to paralysis of this center.

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