a membrane in the eye . 
3 °7 
retina, by which the structure of the latter membrane was de- 
stroyed ; the explanation here given is as sufficient to account 
for the existence of this fluid, as that which attributes it to 
the increased secretion of a serous membrane. 
I take this opportunity of describing the method I adopt for 
examining and displaying these and other delicate parts, a 
method, which though simple, will, I expect, prove an impor- 
tant improvement in the means of scrutinizing the structure 
of animal and vegetable bodies. I procure a hollow sphere 
of glass from two to three inches in diameter, about one 
fourth of which is cut off" at the part where it is open, and 
the edges ground down, so as to fit accurately upon a piece 
of plate glass, the surface of which is also ground ; the object 
to be examined is attached to a piece of wax fastened upon 
the plate of glass and immersed in a basin of water, with the 
cut sphere, which is inverted over it, of course full of water, 
and the whole withdrawn from the basin. The part may 
thus be examined under the most favourable circumstances ; 
it floats in water, the only method by which delicate parts 
can be unfolded and displayed : the globular form of the ves- 
sel answers the purpose of a lens of considerable power and 
perfection, at the same time that it admits light in any quan- 
tity or direction to illuminate the object ; and, what is of the 
utmost importance, a preparation of the greatest delicacy 
may thus be handed round a class in safety. 
