616 JAMES W. BARRETT. 
and was then hardened in alcohol and carbolic acid. The per- 
manganate salt did not harden, and the sections of retina 
prepared in this way were unsatisfactory. 
7. Chromic Acid.—The fresh and opened eye was placed in 
a % per cent. watery solution of chromic acid and was allowed 
to remain there for twenty-four to forty-eight hours. The 
hardening was then completed by the use of the alcohol and 
carbolic acid solution. If the eye was left more than forty- 
eight hours in the chromic acid solution difficulty was expe- 
rienced both in staining and in the preparation of sections (on 
account of brittleness). Sections so prepared were usually 
very serviceable in showing the structure of all the layers 
except the rod layer. 
8. Chloral Hydrate.—The fresh and opened eye was placed 
in a 10 per cent. solution of this salt for two to seven days; 
the hardening was completed by the alcohol and carbolic solu- 
tion. Chloral did not harden, and in my hands only yielded 
first-class results occasionally. It certainly has the merit of 
preserving the rod layer, and it is quite possible by this method 
to obtain satisfactory specimens with the rods and cones in 
sitd. 
9. Chloride of Gold.—I have made very many efforts to 
obtain sections stained with this salt, but they have not been 
successful. 
The following methods have been employed : 
a. The fresh freely-opened eye was placed in asolution of 1 per 
cent. of the salt for fifteen to forty-five minutes and was then 
transferred to a weak solution of formic or acetic acids, and was 
left there in the dark till the salt was reduced (usually twenty- 
four to forty-eight hours). 
b. The fresh freely-opened eye was placed for one to three 
minutes in weak formic acid, and was then treated as before. 
c. The fresh freely-opened eye was placed for several days in 
a 1 per cent. watery solution of chromic acid. When hardened 
the eye was placed in a neutral or slightly alkaline solution of 
the gold salt for thirty minutes and was transferred to a solu- 
tion of weak formic acid kept at a temperature of 30° C. in the 
