PLATE s 
Figures 38 and 45 are magnified about 1,000 diameters; figures 39 
and 40, 1,450 diameters; figures 41 and 42 about 1,100 diameters. 
Fic. 38.—Visual elements as seen in a radial section of the retina 
of Necturus, showing different~ staining qualities. The ellipsoids of 
single cones and of far cones stain alike. Those of the near cone 
and of rods also stain alike. All outer segments of cones stain alike 
The outer segments of rods contain a blue staining reticulum in additior. 
to the substance that stains with fuchsin. ‘The material was fixed in 
corrosive-acetic mixture and stained with aniline blue, fuchsin, orange 
G., phospho-molybdic acid, ete. (Mallory :00). 
Fic. 39—Thin section of a cone from the same material as that 
shown in Figure 38. The substance of the ellipsoid, staining with fuchsin, 
is in the form of globules, the arrangement of which gives some suggestion 
of rows. Superficial fibrils staining blue are visible between the ellipsoid 
and the nucleus. 
Fic. 40—A field of the outer segments of visual cells from the same 
material as that shown in Figure 38. The superficial blue fibrils are 
seen as dots in both rods and cones. One rod is drawn in detail. In 
this the peripheral portiors are much vacuolated and devoid of substance 
staining in fuchsin. 
Fics. 41, 42.—Isolated outer segments of rods in natural fluid from 
the eye, but containing a trace of ammonium-molybdate followed by 
toluidin blue. A central portion has taken up the blue stain in a some- 
what irregular war. The irregularity is probably due to a post-mortem 
disintegration. In Figure 42 the central staining core projects beyond the 
peripheral substance. 
Fic. 43—A field containing fresh isolated rods and a cone in eye- 
fluids as seen with a polarizing microscope having a gypsum interference 
plate. The latter when inserted between the Nicol prisms gives as a 
field color, red of the first order, while bodies in the field possessing 
polarity are yellow or blue according as their axes of maximum elasticity 
lie at right angles or parallel, to the a axis of the gypsum plate. This 
test shows that the long axes of the outer segments of both rods and 
cones are in the positive optical direction, indicating the short axis 1s 
that of maximum elasticity. The outer segment of the cone shows 
a much less decided reaction than that of the rod, while the inner 
segments of both show the neutral field color. 
Fic. 44.—A single medullated nerve fiber from the sciatic nerve 
of the frog as seen by the same color test as that described under 
Figure 43. The medullary sheath shows a very decided double refraction 
with the axes of minimum elasticity radial with respect to the axis- 
cylinder. The reaction of the axis cylinder, though not decided in this 
instance, is discernible as opposite in character to that of the sheath. 
(Continued on next page.) 
