chemical Nature of the Humours of the Eye. 199 
talline, is in the inverse ratio of the diameter of the eye, taken 
from the cornea to the optic nerve. Should further experiments 
show this to be a universal 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 specific gravity of the aqueous and vitreous 
humours, no particular precaution is necessary, except that they 
ought to be as fresh as possible. But the crystalline humour is 
not of an uniform density throughout; it is therefore essential, 
that attention be given to preserve that humour entire for this 
operation. I found the weight of a very fresh crystalline of an ox 
to be 30 grains ; and its specific gravity was, as I before stated, 
10765. I then pared away all the external part, in every direc- 
tion, till there remained but 6 grains of the centre; and the 
specific gravity of these 6 grains, I found to be 11940. From 
this it would seem, that the density increases gradually, from the 
circumference to the centre. 
It is not surprising that the crystalline humour should be 
subject to disorders, it being wholly composed of animal matter 
of the most perishable kind. Fourcroy says, that it is some- 
times found osseous in advanced age. Albumen is coagulated 
by many methods ; and, if we suppose that the same changes 
can take place in the living eye as in the dead animal matter 
of the chemists, it will be easy to account for the formation of 
the cataract; a disorder which cannot be cured but by the 
removal of the opaque lens. If a sufficient number of observations 
were made respecting the frequency of the cataract in gouty 
habits, some important conclusions might be drawn, as to the 
influence of phosphoric acid, in causing the disorder, by the 
common effect of acids, in coagulating albumen. 
