602 HOWARD. [Vot. XIX. 
the fresh material. Treatment by this method did not yield 
well preserved outer segments. A 40 per cent. aqueous solu- 
tion destroys the double refraction of outer segments of 
rods. A 4 per cent. aqueous solution gives reversal of 
reaction for outer segments. The form of the rod is not 
well preserved. 
Nitric Acid (10% ).—This reagent causes the outer seg- 
ments of the rods to elongate to almost double their original 
length, but apparently they retain their former volume. This 
change is accompanied by a reversal of the colors in the light 
test and a loss of transparency by granulation. 
Picric Acid seems to cause the loss of double refraction in 
the outer segments of rods; in polarized light with the gypsum 
interference plate they show the red “field color” at all angles. 
Mercuric Chloride (saturated aqueous  solution).—A 
reversed color reaction in polarized light occurs in outer 
seginents when placed in mercuric chloride. Voluntary muscle 
seems to be unchanged in this optic character when sub- 
jected to the same treatment. However, after Jong fixation 
muscle shows the same results as the rods do. 
A study of sections of the retina fixed by this method 
shows a very fair preservation of the general form of the 
elements, with slight contraction. The nucleoplasm is notice- 
ably contracted, so as to be quite generally separated from 
the nuclear membrane. Staining seems to bring out less of 
the fine detail than is obtainable by some other fixatives. 
The membrana limitans externa of the retina is more dis- 
tinct than with other fixatives. 
Mercuric Chloride + 5% glacial acetic acid gave reversal 
with polarized light. A detached outer segment of a rod 
under observation when the fluid was admitted, showed 
suddenly a central axis, as if that portion were first affected, 
then the rod curled into a horse-shoe shape. Sections fixed 
in this fluid have been described above under “Permanent 
Preparations.” 
Zenker’s Fluid—With this reagent preservation is good 
a 
