i'O Chemical Xature of the Humours of the Ej/e. 



Vltrenvs Humour. 



I pressed the vitreous humour through a rag. In order to 

 free it from its capsules ; and in tliat state, by all the experi- 

 ments I could make upon it, I could not perceive any dif- 

 ference between it and the aqueous humour, either in its 

 specific gravity (which I found to be lOOyO, like that of the 

 other,) or in its chemical nature. 



M. Fourcroy mentions a phosphate as contained in these 

 humours; but I could not perceive any precipitation by 

 muriate or nitrate of lime ; nor did the alkalis denote the 

 presence of any earth, notwithstanding M. Fourcroy's as- 

 sertion of that fact. 



hujNiAx eve. 



I could not procure a sutficient fjuanlltv of these, fresh 

 enough to multiply mv experiments upon them. However, 

 by the assistance of Mr. Carpue, surgeon to his majesty's 

 forces, I fully convinced mvself that the humours of the hu- 

 man eye, chemically considered, did not contain anv thing 

 ditlerent from the respective humours of the eves I had exa- 

 mined. The aqueous and vitreous humours contained wa- 

 ter, albumen, gelatine, and nmriate of soda ; and the crvs- 

 talline humour contained only water, albumen, and gela- 

 tine. The specific gravity of the aqueous and vitreous hu- 

 mours I found to be 10053, while that of the crystalline 

 was 10790. 



EVES OF OXEX. 



I found the eyes of oxen to contain the same substances 

 as the respective humours of other eyes. The specific gra- 

 vity of the aqueous and vitreous humours is 100S8, and 

 that of the crystalline 107G5. 



What is particularly worthv of notice is, that the differ- 

 ence which appears to exist between the specific gravity of 

 the aqueous or vitreous hinnour and that of the crystalline, 

 is much greater in the human eye than in that of sheep, and 

 less in the eye of the ox. Jlence it would appear that the 

 ditfercncc between the density of the aqueous and vitreous 

 humour and that of the crystalline, is in the inverse ratio of 

 the diameter of the eye, taken from the cornea to the optic 

 nerve. Should further experimcTits show \\\\i to be a uni- 

 versal law in nature, it will not be possible to deny that it 

 is in some degree designed for the purpose of promoting 

 distinct vision. 



In taking the spcdfic gravity of the aqueous and vitre- 

 ous humours, no particular precaution is necessary, except 

 that tliey ought to be as fresh as possible. But the crystal- 



3 Hue 



