This disposes of the first idea, that the presence of the lens in the vitreous would account for the phenomenon. Neither experience nor theory support the view that an alteration in refraction is responsible for the appearance. We are thus narrowed down to the conclusion that the pigmentary change is an accompaniment of the development of cataract in a certain percentage of eyes, and is independent of the method of operation resorted to for the relief of that condition. In this connection, two interesting observations deserve record, as they possibly throw an important sidelight on the question at issue: (1) Lenses extracted in India differ from those met with in European practice, in the amount of colouring matter they contain. A very large percentage of them are stained with pigment, which is frequently of a deep tint. Many of them are dark brown, and a few are almost black. (2) Cyanopsia is of extraordinarily frequent occurrence as a sequela during convalescence after cataract extraction in Madras. Over 50 per cent. of the patients complain of it, whilst only 2·8 per cent. suffer from erythropsia, and 1·2 per cent. from yellow or green vision. We thus find two very striking differences between Western and Eastern cataract experience, and there is, to say the least of it, a strong suggestion that the phenomena are closely connected with each other--in other words, that the cyanopsia is a result of the retina becoming tired out for the perception of yellow by long exposure to a tropical light filtering through a brown or yellow lens. There is also a strong presumption that the coloration of the lenses is due to a migration of pigment, which takes place during the development of cataract in the East, a migration which is directed from the pigmentary layer of the retina, and probably from other parts as well, towards and into the developing cataracts. If the above hypothesis is correct, we might assume that the retina is more likely to be functionally affected in an adverse sense when deprived of the protection ordinarily afforded by its pigmentary layer. In order to test this, the author some years ago made a systematic examination of a large number of eyes from which cataracts had recently been removed, with the object of ascertaining whether cyanopsia was complained of, principally or only, in those cases in which the choroidal vessels were seen to stand out with unusual distinctness under ophthalmoscopic examination. The depth of discoloration of the lenses was at the same time noted in each case. The results obtained appear to favour the views we have above enunciated, but they were not sufficiently conclusive to justify the formation of a decisive opinion. It must be remembered that, whilst a tinge of colour runs through most of the cataractous lenses removed in the East, there are very wide variations, not only in the depth of the pigmentation, but also in the actual coloration present. Some of them