618 JAMES W. BARRETT. 
2. Osmicacid . 2 per cent. 
Chromic acid . + 29 
a alcohol, } Bqual parts. 
With these solutions the layers of the retina, exclusive of 
the rod layer, were very fairly prepared, but in that layer 
shrinkage was produced. 
d. The fresh and opened eye was placed in a solution of 
Osmic acid . . + per cent. 
Chromicacid . 2 ,, 
Water. 
for twenty-four to thirty-six hours, and was then transferred 
to the alcohol and carbolic solution and treated as before. By 
this method the most uniform and certain results have been 
obtained. All parts of the retina were fixed and preserved in 
a manner superior to that produced by any of the other re- 
agents used. 
Mode of Staining.—It is quite possible to stain sections 
of retina if they have been prepared by the celloidin method, 
but if they are to be prepared by the paraffin or cacao butter 
method, the retina must be stained in bulk before it is 
embedded (at least with the nuclear stain). _Two nuclear stains, 
logwood and carmine, have been chiefly used, there being objec- 
tions to the use of theanilines. Kleinenberg’s logwood and the 
alcoholic borax carmine already described were selected ; if 
thick sections are required (as in searching for blood-vessels) 
the carmine is preferable because it is a transparent stain, 
whilst if the thinnest sections are required nothing equals 
Kleinenberg’s logwood. 
Retinas should be left in the carmine about two days and in 
the logwood from twelve to twenty-four hours. The exact time 
depends much on the hardening agent which has been used, 
and must vary for each retina. If only very thin sections be 
cut a moderate amount of overstaining with logwood does no 
harm whatever. 
In order to examine Miillerian fibres or blood-vessels the 
sections of the retina which have already been stained in bulk 
