MICROSCOPICAL TECHNIQUE, ETC. 171 
purpurin the protoplasm, and the latter stain will not 
wash out in water or spirits to any great degree. 
There is in some minds a suspicion of the permanency 
of this stain ; but at any rate it keeps well in balsam 
for several years. 
This dye, benzo-purpurin, stains cell-protoplasm so 
well that we have used it for leprous tissue, to study 
the relation of the “rods” to the cells, in this way: 
The bacilli were stained in the usual way with carbolic 
fuchsin, the tissue decolorised in mineral acid, the 
nuclei stained with acid hsematoxylin, and the cells 
with very dilute benzo-purpurin, the result being ex¬ 
tremely instructive and useful. Such subjects as require 
special staining for their demonstration must, of course, 
be treated as their nature demands; but this may be 
said, if sections are well cut and the staining process a 
good one, and well carried out, there will be little or no 
difficulty in photographing the preparations. With 
Weigert’s stains for the central nervous system, and 
with any of the well-known modifications of that method, 
we have found no trouble in getting good photo-micro¬ 
graphs when the sections have been reasonably thin. 
So, too, with the Ehrlich-Biondi, so much used at 
one time ; and so with all the variations of the carmine 
stains. 
For bacteriological preparations the point, as already 
stated, is to have the organisms discretely stained and 
well washed ; but it is also necessary with the blue 
and violet dyes to have the stain dark. Gentian_or 
even methyl-violet—photographs beautifully when the 
