No. 3.] VISUAL CELLS ANG VERTEBRATES. 603 
and fixation generally satisfactory, so far as I have observed. 
I have used it but little. 
Petrunkevitsch’s Fluid.—* This mixture causes a great deal 
of vacuolation in the outer segments of the rods. 
Perenyt's Fluid causes outer segments to contract trans- 
versely and lengthen, probably preserving the same volume. [ 
should attribute this effect to the contained nitric acid, which, 
when used alone, produces similar results. Vacuolation is 
greater than in mercuric chloride plus 5 per cent. acetic acid. 
The most marked effect in the whole visual cell is the vacu- 
olation and consequent general expansion of the paraboloid. 
A similar effect is produced in the nuclei. The outer segments 
of cones seem to be as well preserved by this method as any 
I have seen, judging by external form, and from comparisons 
with fresh material. 
Golgi’s Rapid Process —This method gave some indications 
of selective impregnation in the details of the elements. I 
was surprised and interested in this, but did not have the 
opportunity to carry on trials until complete impregnation 
was obtained. In other material treated by this process I 
have obtained elements so densely impregnated that there was 
little opportunity to make out finer cell details. The published 
results of other workers (Ramon y Cajal, Dogiel, et al.) 
who have used this method on the visual elements show the 
whole cell impregnated. On account of these results, I did 
not consider the method favorable for my special problem. 
Drying.—Fixation by drying at a high temperature, in the 
manner of making “blood preparations,” breaks up the outer 
segments into short pieces, but these appear in natural con- 
dition as to transparency and form. Light tests give normal 
reaction after twenty-four hours. Outer segments dried at 
*Formula: 
AON COMO ts sae otics nbs dia) sche eysuet eee SOONCHC: 
GlACtPy ACEC stone ee aie cae ee eecne 00°C: @ 
INGERICE PAC TAN arm okie seer eee oe eee LOCC? 
Mercutio Chlonideltem sameeren litres 50 g. 
