MICROSCOPICAL TECHNIQUE, ETC. l6l 
Photography rightly prides itself on its accuracy, and 
if, in our procedure preliminary to the photography, we 
alter the appearance of our objects, then our photo¬ 
graphy simply accentuates and perpetuates a falsity. 
It is true that every method of preparing tissues for 
microscopic observations alters more or less the appear¬ 
ance of the object; but it is in practice necessary to 
prepare our tissues in some way and to some extent ; 
our duty, then, is to alter them as little as possible. 
This duty is kept firmly before our eyes in the neces¬ 
sarily brief remarks that follow. 
The usual plan for fixing substances, liquid or semi¬ 
liquid , spread on the cover-glass—to prevent the 
substance from being washed off in later operations—is 
to heat the glass to such an extent as to coagulate the 
albumen ; and doubtless this is effective and safe in 
careful and competent hands. But many a preparation 
has been spoiled by this treatment ; and an equally 
effective and much safer plan is to immerse the cover- 
glass for even a few seconds in saturated mercury 
perchloride. We have never known a substance con¬ 
taining any albumen washed off after this treatment, 
and the sublimate acts as a mordant for the stains that 
usually follow. (If the substance contains no albu¬ 
minous matter the heating will not fix it to the glass.) 
In almost all cases it will be found best to immerse 
solid tissues, as soon as possible after removal, in a 
similar solution of sublimate; sodium chloride or acetic 
acid may be added to the water for solution, but we 
find no need for it; and it seems to make the future 
