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XXIV] severity, being characterized by intense headache, a rapid full pulse, a pungent dry skin, intolerance of light, sound, and movement, and occasionally by vomiting or delirium. This condition suggests meningeal congestion, possibly inflammation. The acute phase may be quickly recovered from, or it may prove very persistent and last for days or weeks. It may leave no injurious effects; or it may be followed by a variety of transient or more permanent morbid nervous phenomena. Among the sequelæ authors have mentioned tremor, loss of memory, amaurosis, deafness, various paretic conditions, epilepsy, insanity, persistent headache, recurring headache, dyspeptic conditions. How far these sequelæ are entirely attributable to sun-exposure, or how far they depend on other diseases, as syphilis for example, the local cerebral manifestations of which may have been provoked, though not actually caused, by the suntraumatism, it is not always easy to say.

The morbid anatomy, as well as the clinical symptoms, indicates meningitis as a feature of these instances of reputed sun-traumatism. Authors refer to thickenings and opacities of the meninges, and even to thickening and roughening of the calvarium.

Many speculations have been advanced as to the pathogenesis. Manifestly it is not altogether, if at all, a question of caloric, for such effects do not result from exposure to the heat of a furnace, however intense. There appears to be some special element in the solar spectrum capable of injuriously affecting the tissues, particularly if they have not become gradually habituated to sun-exposure. That some such element does exist is proved by the phenomena of sun-erythema, of that form of skin pigmentation known as sun-burning, and, possibly, of leucodermia. The sensation of distress brought on by exposure to a hot sun, which is quite a different sensation from that produced by the heat of a fire, points in the same direction. In this connection we are forcibly reminded of the phenomena of the actinic rays of the solar spectrum, and of the remarkable tissue changes induced by the Kontgen rays.