During the last decade, physiologic investigation has revealed many new facts with regard to the activity of the capillaries. Our knowledge is as yet fragmentary and incomplete, but enough has been learned to emphasize the great importance of this portion of the vascular system.
From the standpoint of tonus, the capillaries may be affected either by spastic or contraction reactions, or by atony or dilatation reactions. The clinical manifestations usually include a combination of these capillary responses, although pure reactions are seen. The atonic capillary is usually seen in the so-called vasoneurotic constitutional states, and less often in persons with apparently normal vasomotor mechanisms. Müller1 has described the capillary picture in the vasomotor neuroses. This varies markedly from the so-called normal capillary. He emphasized the following points:
1. Spastic and Atonic Reactions of the Capillary.
—The tonus of the capillary is evidenced by changes in the lumen of the vessel,