248 Proceedings of the Royal Physical Society. 
of Petit stands out as a red ring around the margin of 
the lens. 
The specimen is prepared in the following manner :— 
The muscles and fat surrounding the eye of an ox are 
removed, and an incision made along the equator of the eye- 
ball, so as to divide the sclerotic into two parts, one being 
attached to the optic nerve, and the other to the cornea. 
The beginning of the cut is made with the knife, so as to 
allow one blade of the scissors to be inserted between the 
sclerotic and choroid. The cut is then completed with the 
scissors, great care being taken that the vitreous is not 
punctured. The next stage consists in turning the two parts 
of the sclerotic inside out, so as to allow more room for the 
division of the choroid. The choroid is divided in a similar 
manner with the scissors, and the vitreous together with the 
lens and Canal of Petit allowed to fall out, bursting through 
the retina. Any pigment from the ciliary processes may be 
brushed off from the suspensory ligament of the lens with a 
camel-hair pencil under water. The canal may then be 
injected with a hypodermic syringe, previously filled with 
melted carmine-gelatine. The needle of the syringe is 
pushed through the anterior wall of the canal, more or less 
horizontally, close to the margin of the lens, and the gelatine 
forced into the canal. It may flow all the way round the 
lens, but, as a rule, it is better to inject the canal at twice, 
withdrawing the needle after the injection has flowed half 
way round the canal, and re-inserting it where the fluid 
stopped, so as to inject the remainder. The specimen is 
best preserved in a mixture of equal parts of glycerine and 
methylated spirits. 
