162 
PRACTICAL PHOTO-MICROGRAPHY. 
elimination of the sublimate more difficult. Granted 
that, for the central nervous system, and where it is 
important to preserve blood in its relation to other 
tissues (Woodhead), Muller’s fluid maybe preferable; 
and for certain purposes Klein’s fluid (chromic acid and 
spirits) or Foa’s (sublimate and potass, bichromate) 
may be useful or necessary; still, for general purposes, 
nothing is probably so good as saturated sublimate. 
The pieces of tissue are to soak in this from twelve to 
twenty-four hours, acccording to their size. They are 
then washed from eight to twelve hours in running 
water, or in many changes of dilute spirits not under 
thirty-five per cent. For washing in water, a china tea¬ 
pot may be used; the lid-hole covered with muslin, the 
water run into the spout briskly from the tap. The 
strength of the spirit, after washing, is gradually in¬ 
creased up to seventy per cent.; and in this the tissues 
are kept till the actual preparations for section-cutting 
are begun. 
In preparing tissues for physiological or pathological 
investigation we usually have two ends in view: first, 
to study the tissues in general or their relations to each 
other and to surrounding tissues ; and, second, their 
intimate characters, or histology. Thus, in pathology, 
we wish to know the relation of the diseased parts to 
the surrounding healthy tissues, and we also wish to 
discover the histological facts of the diseased tissue. 
For the first purpose it is necessary to take a bit of the 
abnormal part where it abuts on the normal, and this 
bit should be as large as can be conveniently manipu- 
