170 
PRACTICAL PHOTO-MICROGRAPHY. 
stain in the tissues, and gives it the blue colour which 
is a sure sign of the fixation. 
The next step is to “ counter-stain ” the section, 
though this is a term not wholly applicable ; for what 
we do is to stain, equally discretely, other tissues with 
other dyes. Make saturated aqueous solutions of “ acid 
rubin ” and “ orange G ” (Griibler), and mix them in the 
proportions of ten of orange to one of rubin, and then 
dilute the mixture with water till it stains sections dark 
red in about five minutes. After the sections are 
stained in this, wash in water till they lose no more 
colour in the water, then wash in spirit, then dehydrate, 
clear in mineral naphtha, and mount in xylol or benzole 
balsam. Instead of the naphtha we may use Weigert’s 
solution, one part absolute phenol to three parts xylol, 
but clove oil should be avoided for every tissue, every 
stain, and every purpose. Now it frequently happens 
that the orange which is intended to stain “ proto¬ 
plasm ” is all washed out by these operations, and 
search was made for some protoplasmic stain which 
would not wash out so readily. We finally adopted 
benzo-purpurin (Squire). A “stock” solution is made 
as follows : 
Benzo-purpurin ... ... 1 part. 
Alcohol ... ... ... 20 parts. 
Water to . 100 ,, 
To make the stain for use, take of the stock benzo- 
purpurin 10 parts, of the saturated rubin solution 
4 parts, and make up with water to 100 parts. The 
rubin will stain the connective tissues, and the benzo- 
