HISTOLOGICAL ELEMENTS RETINA NECTURUS 415 
nerve, and in another set parallel to the dorso-ventral plane, 
and passing through the optic nerve. Series of sections 6u thick 
were made through the entire thickness of the retina tangential 
to the surface of the eyeball in the anterior, posterior, dorsal, 
and ventral regions and in the fundus. The sections were stained 
in Heidenhain’s iron haematoxylin as a base, and in a 70 per 
cent alcoholic solution of eosin as a counter stain. Thirty minutes 
in the mordant (2 per cent ferric alum) and one hour in the hae- 
matoxylin gave very satisfactory results. The excess of stain 
was washed out in ferric alum of the same strength as the mor- 
dant, and the washing was continued until all traces of the haema- 
toxylin had disappeared from the outer segments of the rods 
and from the reticular layers. At this stage the nuclei of the 
outer and inner nuclear layers and of the ganglionic layer were 
clearly defined and light blue in color. The nuclei of Miiller’s 
fibers were stained a deep blue to blue-black and contrasted 
sharply with the lighter blue of the surrounding nuclei. Control 
was kept over the process of destaining by examining the slides 
every few seconds under the microscope. Two minutes in the 
counter-stain were sufficient to color the outer segments of the 
rods bright red. The outer and inner reticular layers appeared 
as broad red fibrous bands separating the inner nuclear layer 
from the outer nuclear and the ganglionic layers, respectively. 
The strands of Miiller’s fibers, which stretched radially outward 
from the internal limiting membrane, were stained an intense 
red. It is clear that the selective qualities of the stains employed 
rested primarily with the haematoxylin, for in the process of 
reducing the over-stain of the base the outer segments of the 
cones, the nuclei of Miiller’s fibers, and the ellipsoids, retained 
their color longer than the other elements, thus indicating their 
greater chemical affinity for the basic stain. Although the suc- 
cess which attended fixation in picro-sulphurie acid and double 
staining with haematoxylin and eosin made other methods super- 
fluous, nevertheless some entirely successful preparations were 
refers to that part of the eyeball which is nearest the anterior end of the animal 
(‘internal’ in human anatomy), ‘dorsal’ to that part which is nearest the dorsal 
midline (‘superior’ in human anatomy), etc. The deep part of the eyeball, often 
called the posterior part, is here referred to as the ‘fundus.’ 
