Page:The Harveian Oration,1902.djvu/58

 alia profuse perspiration, horripilation, and movements of the abdominal and pelvic viscera, which can rarely, if ever, be reflexly induced by any degree of peripheral stimulation. In its more intense forms fear may for ever arrest the heart-beat or so break down all the protective mechanism of the organism that flight, defence, or other means of adaptation are rendered impossible, and the animal falls an easy victim to the danger assailing it.

When we inquire by what mechanism the centres of thought and feeling influence the heart and blood-vessels—whether there are cortical cardiac and vaso-motor centres properly so-called, or whether the cerebral hemispheres act only indirectly upon the cardiac and vasomotor centres of the medulla oblongata, we come upon a subject on which, in the present state of our knowledge, it is necessary to speak with caution, avoiding too confident or dogmatic assertion. Several observers have described variations in the rate of the heart and tone of the blood-vessels as resulting from irritation of various portions of the cerebral hemisphere, particularly the motor area or