PREPARATION OF EYE FOR HISTOLOGICAL EXAMINATION, 615 
No good results followed, chiefly because of the firm con- 
sistency of the vitreous. A more simple method was then 
adopted ; the length of the incision was made equal to a 
quarter of the circumference of the eye, and the eye was 
then placed in the fixing solution. At the end of thirty 
minutes or less the posterior part of the eye was removed by 
enlarging the original incision with sharp scissors. By this 
means the fixing agent obtained access to the retina rapidly, 
and detachment of the retina was prevented. 
3. Picric Acid.—The fresh and opened eye was placed 
in a saturated watery solution of picric acid for three days, 
and the hardening was then completed in alcohol and carbolic 
acid. By this fixing agent everything was rendered intensely 
hard but rather brittle. Sections of retina prepared in this way 
were very serviceable in showing the structure of the nerve- 
layers of the retina, but the outer nuclear layer and the 
rod layer were profoundly altered. The nuclei (with a twelfth 
oil immersion lens) showed a remarkable crenation, whilst 
similar nuclei in another eye prepared with such a reagent as 
osmic acid showed no such crenation. By the use of picric 
acid, however, it was possible to trace the Miillerian fibres at 
all events as far as the outer reticular layer, since the previous 
immersion of the retina in picric acid seems to intensify the 
eosinophilous property which those fibres exhibit. 
4, Carbolic Acid.—The fresh eye, prepared as before, was 
placed in a 2 per cent. watery solution of carbolic acid for a 
week, and was then hardened in alcohol in the usual manner. 
Carbolic acid itself does not harden. By this means fair speci- 
mens of all parts of the retina were occasionally obtained. 
5. Zine Chloride.—The fresh and opened eye was placed 
for a week in a 1 per cent. watery solution of this salt and was 
then removed to the alcoholic solution of carbolic acid. The 
zinc salt did not harden, and seemed to destroy the outer 
layers of the retina, but its action on the Miillerian fibres was 
similar to that of picric acid. 
6. Permanganate of Potash.—The fresh and opened eye 
was placed in a 2 per cent. solution of this salt for seven days 
