600 HOWARD. [Vor. XIX. 
was that the fluid was probably isotonic with the cell 
fluids. When this solution was introduced at the edge of the 
cover-glass a remarkable reaction of the outer segments of 
the rods was observed. An individual rod was watched under 
an eye-piece micrometer, and the following changes in dimen- 
sions noted. Before admission of fluid the length of the rod 
was 6 divisions; at entrance of the fluid it contracted rapidly 
to 3 divisions; after which it slowly lengthened to 7 divisions. 
The experiment was repeated using another animal and the 
time noted. Before the admission of the fluid the length 
was 6 divisions; at entrance of the fluid contraction began 
and lasted for one minute, until a length of 4 divisions was 
reached; after this, the rod lengthened to 8 divisions, the 
period of lengthening being 7 minutes. 
Physiological Salt Solution (349% ).—Outer segments of 
rods after remaining four hours in this solution showed 
normal positive reaction in polarized light. In this solution, 
however, a majority of the outer segments showed disinteg- 
ration and distortion of form, with no refraction at all. 
After three days such outer segments as were still sufficiently 
intact to show any double refraction, gave reversed color 
reaction; 1. e., they were anisotropic and negative with respect 
to their long axes. 
Amniotic Fluid.—This was obtained from pig embroys and 
was kept in sterilized bottles with a small piece of thymol 
as a preservative. Outer segments of rods rapidly disin- 
tegrated in this fluid, possibly because of the presence of 
thymol. 
Egg Albumen.—As much of the fluid portion of this sub- 
stance as would easily pass through a strainer of bolting 
silk proved as satisfactory an examination medium as the 
fluid from the eye. About 10 c.c. of liquid albumen can be 
obtained from a single egg. 
‘2. Fixing Agents. 
In giving the results of tests with fixing fluids I have 
included an account of the unsuccessful trials as well as the 
