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The use of the black rete mucosum of the negro is a subject which has fruitlessly engaged the attention of the physiologist. The author’s mind was directed to this inquiry by the circumstance of a silver fish having its back scorched in consequence of the removal of some trees which shaded the pond in which it lived; this recalled to Sir Everard’s recollection the circumstance of his having suffered severely from the scorching sun of the tropic, upon parts of the body protected from the direct rays of the sun by thin white linen, and led him to suspect that the noxious effects were derived not, as has commonly been supposed, from the mere heating power of the sun’s rays, but from the joint agency of heat and light: he therefore made certain experiments, detailed in this paper, which show that the face and hands may be exposed to a temperature of 100° to 120°, without producing pain, provided light be excluded; but that if the same, or even an inferior degree of heat, be produced by the direct light of the sun, it scorches and elevates the cuticle in blisters; this effect is prevented by covering the hand or face with thin black kerseymere, and the same purpose is attained by the black rete mucosum of the negro. In these cases perspiration comes on, which it does not in the former, and the surface, though actually hotter, is uninjured. Nature has provided a similar defence from the injury of light, by placing a black pigment at the bottom of the eye of those animals who are exposed to the intensity of the sun’s rays; whereas in the inhabitants of shady and dark situations the pigment is either pale, or altogether wanting.

On the black rete mucosum of the negro, being a defence against the scorching effect of the Sun’s rays