PRELIMINARY OBSERVATIONS ON SOME 
CHANGES CAUSED IN THE NERVOUS TISSUES 
BY REAGENTS COMMONLY EMPLOYED TO 
HARDEN THEM. 
HENRY H. DONALDSON, 
PROFESSOR OF NgEuROLOGY, UNIVERSITY OF CHICAGO, 
Introduction, — In determining pathological changes in ani- 
mal tissues, the normal histological appearances are used for 
the purposes of comparison. These appearances, it is presumed, 
are to be found in animals suddenly killed while in full health. 
As a matter of fact, the tissues obtained from such animals 
are not exactly similar, and it is now known that there area 
number of secondary conditions which must be taken into 
account. 
The normal tissues certainly vary, according to the age of 
the animal, and the physiological conditions of rest and fatigue 
just preceding death. 
Probably this does not exhaust the list, but these two points 
are the only ones thus far demonstrated. 
The methods of treating tissues for the purpose of histo- 
logical examination are admitted by all investigators to produce 
more or less marked variations when compared with fresh 
material. 
By these methods both the relative and absolute size of the 
different elements and their reactions to staining fluids and 
other reagents are modified. 
All this is true, quite apart from the many changes which 
may be induced by careless or incautious handling. 
One of the most disturbing reagents is the hardening fluid, 
and it is to some of the effects of hardening fluids that we wish 
in this paper to direct attention. 
The study of this matter has two objects in view: first, to 
determine what changes are induced by the hardening reagents 
