V. Observations on the chemical nature of the humours of the eye

The functions of the eye, so far as they are physical, have been found subject to the common laws of optics. It cannot be expected that chemistry should clear up such obscure points of physiology, as all the operations of vision appear to be; but, some acquaintance with the intimate nature of the substances which produce the effects, cannot fail to be a useful appendage to a knowledge of the mechanical structure of the organ. The chemical history of the humours of the eye, is not of much extent. The aqueous humour had been examined by Bertrandi; who said, that its specific gravity was 975, and therefore less than that of distilled water. Fourcroy, in his Système des Connoissances chimiques, tells us, that it has a saltish taste; that it evaporates without leaving a residuum; but that it contains some animal matter, with some alkaline phosphate and muriate. These contradictions only prove, that we have no accurate knowledge upon the subject.