No. 3.] VISUAL, CELLS? IN VERTEBRATES. 601 
more satisfactory ones, since the account of failures may at 
least save the time of other workers. However, in cases 
where a fluid has been unsuccessful in one animal it does 
not necessarily follow that it will be inapplicable to the same 
tissue in another animal, though the probabilities are against it. 
Again, slight modifications of a formula, or its method of 
application, might meet the requirements. 
Osnuc Acid Vapor.—Outer segments of rods show a 
reversal with polarized light after treatment with this 
reapent: The tints are more brilliant- than “normal 
and the blue phase has a decided greenish cast. The 
permanent preparations made by this method have already 
been described (Pl. 4, Figs. 33-37). The excessive blacken- 
ing of the outer segments and their contraction are char- 
acteristic of long fixation. Short fixation gives appearances 
much like the fresh condition, but with a slightly brownish 
color. 
Osnuc Acid, ¥%2% Aqueous Solution.—The outher segments 
were reversed in color when seen in polarized light; curling, 
breaking transversely, and lengthening occurred commonly 
in the outer segments; notwithstanding these results many 
segments were well preserved. Among the latter, many were 
observed which gave with oblique light alternating light and 
dark bands. 
Vom Rath’s Fluid.—As already stated on page 5709, prepar- 
ations fixed in this fluid show an exaggerated shrinkage in 
leusth* CPi 4) Fiee32)): 
Flemming’s Fluid (strong formula).—The outer segments 
were poorly preserved by this method, but the superficial 
fibrils were brought out plainly. 
Absolute Alcohol.—Double refraction is destroyed; 7. e., 
with light tests the outer segments become quite transparent 
and of the same color as the red field. 
Formaldehyd.—In preparations made by exposure to the 
vapor of formaldehyd the “optical axes,’ as shown by 
the color reaction, were reversed as compared with those of 
