604. HOWARD. [VoL. XIX. 
room temperature disappear in a few hours, apparently by 
deliquescence, leaving a drop of liquid. 
3. Lntra-Vitam Stains. 
Methods were considered for employing “‘intra-vitam” 
stains in the living animal, but as the proportion of successful 
impregnations is likely to be so small, a more practical method 
was sought for. The retina as a whole was placed fresh in 
examination media in which “non-poisonous stains’ were dis- 
solved in very small quantities, or the stain was added while the 
object was under observation to permit of watching the prog- 
ress of the stain. Positive results were obtained with methy- 
len blue, toluidin blue, and hematein. With Congo red and 
some other dyes I obtained no evidence of selective staining. 
Methylen Blue.—A retina was placed fiber layer downward 
so as to leave the rods and cones vertical on the upper side 
and give an end view of these elements. When methylen 
blue is added the outer segments of the cones become imme- 
diately deeply stained, thus the field appears as a mosaic of 
larger white circles, the rods, and smaller blue ones, the cones. 
In teased retinze where the rods are seen laterally, occasional 
individuals may be found with transverse bands stained deep 
blue alternating with light blue ones. In many cases the super- 
ficial fibrils stain blue, and there is some evidence of a central 
axis. The affinity of the stain for only occasional rods is 
probably due to some peculiar condition in the metabolism of 
the element. This selective character is in accordance with 
what has been observed for this method in other parts of the 
nervous system. 
Toluidin Blue.—A retina was placed in fluid egg albumen 
in which was dissolved one three-thousandths by weight of 
ammonium molybdate; after ten to twenty minutes, toluidin 
blue, one three-thousandths in egg albumen, was added. In 
a few minutes the detached outer segments of the rods showed 
a marked differentiation of a central axis or core staining” 
— —— 
es es 
