Mydriasis iris sphincter, composed of circularly arranged muscle fibers, and the iris dilator, composed of radially arranged muscle fibers. The sphincter is innervated by (signaled by nerves of) the parasympathetic nervous system, and the dilator by the sympathetic nervous system. Sympathetic stimulation of the adrenergic receptors causes the contraction of the radial muscle and subsequent dilation of the pupil. Conversely, parasympathetic stimulation causes contraction of the circular muscle and constriction of the pupil. The mechanism of mydriasis depends on the agent being used. It usually involves either a disruption of the parasympathetic nerve supply to the eye (which normally constricts the
What Is a Nation? French citizen has to have forgotten the massacre of Saint Bartholomew, or the massacre that took place in the South in the thirteenth century. While many nations, such as France, begin with a feudal regime such as a monarchy, others, such as the United States and Switzerland, are formed by acts of consensual aggregation. France and many others, however, survived their feudal roots while maintaining their identity. Renan inquires what is the organizing principle? It can't be race, because France is "Celt, Iberian, German...The most noble countries, England, France and Italy, are the ones where the blood is most mixed."