Page:The Harveian Oration,1902.djvu/46

38 tions affecting the outflow from the other sinus. This fallacy, however, is eliminated by Brodie's method. By the injection of adrenalin into the basilar artery of the carefully removed brain, and measurement of the outflow from the torn sinuses, he found that with a moderate amount there was distinct diminution of the outflow, and complete stoppage when the dose of the extract was increased. This appears to afford satisfactory proof of the existence of cerebral vaso-constrictors, though, as compared with those of other organs, their influence is relatively slight ; and there seems, therefore, no further reason for doubting the existence of some intrinsic vaso-motor regulation of the cerebral circulation. The cerebral circulation, however, varies for the most part only passively with the circulation as a whole. The blood is so disposed in the body that it may be temporarily diverted from one region in order to secure a richer supply to another which requires it. It has been calculated that when the body is at rest the thoracic and abdominal organs contain from 60 to 70 per cent, of the whole blood. In the state of activity this percentage is reversed. Thus Ranke estimates that in