As regards the functional disorders of the arterial system, they depend upon the existence of a muscular coat in the walls of these vessels, which was known to Harvey, and of a vaso-motor nerve apparatus, the discovery of which was of comparatively modern date. We are all now-a-days familiar with the expressions arterial tone, arterial tension, and blood-pressure, which undoubtedly have an important pathological and clinical bearing. Vaso-motor disturbances explain a variety of symptomatic phenomena; and are believed by many to account for certain more definite affections, such as Raynaud's disease, angeioneurotic edema, and erythromelalgia; while they are the foundation of attractive hypotheses to explain numerous other complaints.
4. Every student of medicine is familiar now-a-days with the conditions known as thrombosis and embolism, and their effects, immediate and remote, occupy a conspicuous place in the pathology of the circulatory system. No doubt the fact that clotting of blood may take place in the heart and vessels during life has been recognised for a long period, but it is only comparatively recently that thrombosis has been practically studied in its various relationships. Although the conception of embolism can also be traced back to the seventeenth and eighteenth centuries, if not earlier, and a few observations and experiments had been made before his time, it is to the renowned and ever venerated pathologist—
