STAINING AND MOUNTING. IggQ 
alcohol is added the section will suddenly become 
opaque, and for the opposite reason. 
If there is a milkiness on the section or slide when 
the water is poured on it is a sign that the xylol has not 
been completely removed; xylol will not mix with 
water and forms an emulsion with it. If this should 
happen you must give the section another dose of abso- 
lute alcohol. 
It is an advantage to wipe the surface of the slide (of 
course avoiding the section) before going from one fluid 
to another. 
A cardinal rule in dealing with paraffin sections is 
never to let the section get dvy from the moment the first 
dose of xylol is added until the final mounting in 
balsam. 
The methods of staining which are in use are legion, 
and it would be far beyond the scope of this book to 
describe even a few of those which are used in histo- 
logical work and to give indications for their use. It 
will be sufficient to describe (1) a method suitable for 
the diagnosis of tumours, &c., and for ordinary histo- 
logical purposes, (2) a method of staining to demon- 
strate bacteria which stain by Gram’s method, (3) a 
method for bacteria which do not stain by Gram’s 
method, and (4) the process for demonstrating tubercle 
bacilli in the tissues. 
(1). Staining sections for histological purposes :— 
1. Xylol, two lots (to remove paraffin). 
2. Absolute alcohol, two lots (to remove xylol). 
3. Water (to remove the alcohol). 
4. Stain with hematin (or hematoxylin) for ten 
minutes or more according to the nature of the speci- 
men and the condition of the stain. The exact length 
of time can only be learnt by trial, but ten minutes will 
be about right. Rinse in distilled water. 
