Robert Whytt and the pupils.

Abstract

Robert Whytt (1714-1766), Professor of the Theory of Medicine in the University of Edinburgh from 1745 until his death, was one of the great figures of the early years of the so-called Scottish Enlightenment. His investigations of neurological phenomena and their mechanisms in animals and humans led him to enunciate what was in essence the modern concept of reflex action, although he called the phenomenon 'sympathy'. Whytt recognise the peripheral neural mechanisms of the reflex arc and demonstrated that its central element occurred in a limited segment of the neuraxis, where he invoked an 'inner sentinent principle' to mediate neural activity. In 1751, before he had published his formal analysis of the reflex arc, Whytt described the direct and consensual pupillary response to light and the pupillary response to accommodation. On the basis of some simple, well conceived and controlled observations, Whytt showed that the pupillary response was not due to a direct effect of light on the uvea or pupillary muscles, but involved light acting on the retina, leading to an activation of the optic nerve which caused the sentinent principal within the neuraxis to produce pupillary constriction via the activity of the nerves to the pupillary muscles. Ever since, the pupillary reflex has sometimes been referred to as Whytt's reflex.