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Observations on the chemical Nature of the Humours of the Eye. By 

 Richard Chenevix, Esq. F.R.S. andM.RJ.A. Read November 5, 

 1802. [Phil. Trans. 1803, p. 195.] 



After a brief survey of what former physiologists, such as Bertrandi, 

 Fourcroy, Wintringham, and Chrouet, have done in investigating the 

 chemical history of the humours of the eye, in all which he found so 

 considerable a disagreement, and so much obscurity, as to render a 

 new analysis at least useful if not necessary, Mr. Cheuevix proceeds 

 to give us his own experiments. Of these, the first series was made 

 on the eyes of sheep, and the second on the human eye ; and they 

 of course relate to the three humours, the aqueous, the crystalline, 

 and the vitreous. 



The specific gravity of the aqueous humour of the sheep's eye was 

 found to be 10'090, taking that of water as lO'OOO ; and from the 

 results of various experiments, it appears to be composed of water, 

 albumen, gelatine, and of a muriate the basis of which was found to 

 be soda. The specific gravity of the crystalline was equal to 11*000, 

 and was found to consist of a smaller quantity of water than the 

 other humours, but of much larger proportion of albumen and gela- 

 tine; and no essential difference could be perceived between the 

 vitreous humour and the aqueous, their specific gravities, as well as 

 their several chemical properties, being the same. 



From the examination of the humours of the human eye, Mr. Che- 

 nevix convinced himself that they are scarcely in any respect different 

 from those of the sheep's eye. The aqueous and vitreous humours 

 were found to contain water, albumen, gelatine, and muriate of soda ; 

 the latter ingredient alone being wanting in the crystalline. The 

 specific gravities of the aqueous and vitreous humours were 10'053, 

 and of the crystalline 10- 7 90. 



The specific gravity of the crystalline, compared with that of the 

 aqueous and vitreous humours, being much greater in the human eye 

 than in that of the sheep, our author bestows some pages on an in- 

 quiry concerning this phenomenon ; the result of which is, that as 

 the globe of the human eye is smaller than that of the sheep, and 

 hence the distance from the cornea to the retina much shorter, na- 

 ture, in order to preserve the achromatic effect of the eye, rendered 

 the human crystalline proportionably more dense than in other ani- 

 mals. This illustration is confirmed by the examination of the eye 

 of an ox, where the difference between the specific gravities of the 

 humours was as 10'088 to 10'765. 



In examining the eyes of birds, it was found, that, different from 

 those of quadrupeds, the cornea, or the anterior part of the eye, is a 

 portion of a larger sphere than the sclerotica, or posterior part of the 

 ball. It is hence obvious that, in order to produce a proper refrac- 

 tion, it is necessary that the densities of the humours be essentially 

 different. Accordingly, it was found that the specific gravity of the 

 vitreous humour was 11 - 210; while that of the crystalline was no 

 more than 10'392. Whence it appears, that the densities are here 



