176 BULLETIN OF THE 
given poor results. For general purposes Grenacher’s alcoholic borax- 
carmine is excellent. In both embryonic and adult material Czoker’s 
alum-cochineal gave fine nuclear outlines. In the adult eyes, the rhab- 
domes and the cell boundaries were most distinctly shown by Kleinen- 
berg’s hematoxylin. A very faint coloration with this dye gave the best 
results for nerve-fibres. 
For the isolation of the retinal elements two maceration fluids were 
used. A weak solution of chromic acid, as employed by Patten (’86, pp. 
736, 737), gave good results ; but since the mycelium of a fungus is often 
developed in very dilute solutions of this reagent, it can be used only 
when it is carefully watched and its results are controlled by another 
method. It was employed in the following manner. The retina, after 
the removal of the lens and surrounding tissue, was placed for five or ten 
minutes ina }% solution. After this treatment, which slightly hardened 
the tissues, the first solution was replaced by a second of 3%. In this 
the retina remained for three or four days, at the end of which time the 
retinal cells were easily separable. The most satisfactory method of iso- 
lating the cells is to place on a slide in dilute glycerine a small portion of 
the macerated retina, and, having protected it with a cover-glass raised 
on wax feet, to gently tap the cover-glass till the cells are separated. 
One part of 0.2% solution of acetic acid in sea-water mixed with an 
equal volume of 0.04% osmic acid in sea-water, although only partially 
successful as a maceration fluid for the retina in scorpions, is a reliable 
check for the results obtained from chromic acid. 
After the cells have been isolated, the abundance of pigment which 
they contain so obscures their contents that scarcely more than their out- 
lines can be studied. The removal of the pigment is on the whole more 
successfully accomplished before than after isolation. For this process, 
as for simple isolation, the retina should be subjected to the action of 
4% chromic acid for five or ten minutes, and then transferred to a solu- 
tion of 4% potassic hydrate. In this the pigment dissolves, forming a 
reddish cloud. After about a minute the retina should be removed to 
distilled water, rinsed, and transferred to Grenacher’s alcoholic borax- 
carmine. This reagent performs both the office of a maceration fluid and 
adye. In from twelve to twenty-four hours the retinal cells can be iso- 
lated, and present in different regions of the retina three principal condi- 
tions. First, those from the exterior of the retina are seriously altered 
by the continued action of the potash ; second, those from the centre of 
the retina remain almost unchanged, still retaining most of their pig- 
ment ; third, those from an intermediate position, without being other- 
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