Houser, The Neurones of a Selachian. 77 
secured through the use of the chrome-oxalic mixture of GRAF 
(98). This reagent appears to have escaped the general atten- 
tion of microscopists, at least no mention is made of it in the 
fifth edition of LEE (1900). The composition is here given : 
Oxalic acid, 8% aq. sol. . : 200 €.Cc. 
95% alcohol. - : : 150 ¢.C. 
Chromic acid, 1% aq. sol. : 150 c.c. 
Mix in the order as named. 
Quite small pieces of the brain were fixed in this fluid for 
six hours, and the fixing agent was then washed out with 70% 
alcohol. Sections were made by the paraffin method. 
The slide was taken from distilled water, and the steaming- 
hot stain of NissL was poured over the sections, five minutes. 
The excess stain was rinsed away with distilled water for the 
briefest possible time, and the water clinging to the slide was 
absorbed with filter paper. Differentiation with the anilin- 
alcohol of Nisst took but a few seconds, being stopped by 
flooding with oil of cajeput just as soon as the sections took on 
a delicate rose tint. Clearing with the oil of cajeput was aided 
by holding the slide for a few moments in gentle heat. Mount- 
ing was done in colophonium dissolved in xylol. The staining 
is remarkably precise, and the color has shown no tendency to 
fade. 
The counter-staining methods described by HE Lp (’95), 
and by WarRINGTON (’98), were also applied, with certain mod- 
ifications found necessary. The erythrosin mixture of HELD 
was gently warmed, poured over the slide for ten seconds, and 
then washed away quite thoroughly with distilled water. Stain- 
ing was done with either the pure stain of Nissi, or with the 
same diluted with an equal volume of 5% acetone; the results 
did not seem to differ very much. In either case, the stain 
was heated and allowed to act for five minutes. Differentiation 
with 0.1% alum solution for just a few seconds, until the sec- 
tions appeared distinctly red, was followed by a brief rinsing 
with water. The results given by this process have been of 
value as an accessory to the pure methylen-blue stain, but they 
are far from supplanting the original method, 
