STRONG, Technique of Weigert’'s Method. 299 
formalin fixed fibers not being so resistant as fibers impregnated 
with a metallic salt in the act of fixation and hardening. This 
view would seem to be further confirmed by the observations 
above noted (F (4)) where the fibers appeared to be in better 
histological condition when the formalin material was first 
treated with potassium bichromate + osmic than when treated 
in other ways. The superiority of osmic acid in faithfully fix- 
ing medullated nerve-fibers is well known. 
(2) Preparations from pieces mordanted zx foto can often 
be made more brilliant by remordanting the sections before 
staining. When the points noted in (c) have been observed, 
however, this may often be omitted, the gain being insignifi- 
cant and the sections being liable to become brittle. 
(e) The best mordant for WEIGERT-PAL preparations of 
both formalin hardened and other material is probably bichro- 
mate of copper, this apparently excelling WeEIGERT’s chrome 
alum-bichromate mixture. 
Bichromate of copper is a reagent which has some qualities 
to recommend it in neurological work, It was first used by the 
- writer in 1898 and had not been previously applied in histolog- 
ical work as faras I am aware. It is an energetic fixing and 
hardening reagent, more so apparently than any other bichro- 
mate. This indicates its use, either with or without formalin, 
in fixing and hardening foetal brains and spinal cords and as a 
mordant which gives the most brilliant results when the WEI- 
GERT-PaL method is to be used. Asa hardening fluid, the re- 
sults here are confined practically to the above-mentioned (C) 
cord of a 7 months foetus. The material and fibers were per- 
haps somewhat overhardened and shrunken but yielded very 
fine preparations. One hasty trial of this reagent in the method 
of Gore did not produce noteworthy results. 
(f/) Copper bichromate and other bichromates do not give 
good results as mordants (unless, as in the usual method, there 
is remordanting with copper acetate) where the borax-ferricy- 
anide decolorizer is to be used. 
(g) Copper acetate asa mordant invariably yields poor 
