Page:The Harveian Oration,1902.djvu/49

 failure of the cerebral circulation from defective blood pressure is seen in the heaviness and drowsiness which follow a heavy meal, with its consequent dilatation of the abdominal blood-vessels. Some individuals cannot do active brain work in the upright posture, and instinctively adopt such attitudes as favour the flow of blood to the head. The girding of the loins for active effort has its philosophy, according to Roy and Adami, in the compression of the abdominal vessels, which raises the blood pressure and increases the output of the heart.

The influence of the blood pressure on the circulation of the brain naturally leads to a consideration of the influence of cerebral activity, more particularly states of feeling, on the heart and blood-vessels. This is a highly complex problem, and though it has actively engaged the attention of many eminent physiologists and psychologists, the results arrived at are neither altogether definite nor harmonious. The influence of states of feeling on the circulation is, however, so patent that at all