LABORATORY RESEARCH, ETC. 259 
they have been stained by the process we are about to 
mention. 
A preparation ought first to be examined under a 
low magnifying power (from 50 to 100 diameters), so 
as to study the topography of the object, and ascertain 
the points at which the colonies of microbes may be 
sought amid the tissues of a section, or of the matters 
in suspension in the liquid. 
We should then go on to a higher magnifying 
power (for example, to-from 500 to 700 diameters), 
making use of the simple light of the mirror; and we 
should ultimately come to, the highest magnifying 
powers (from 1000 to 1500 diameters), using immer- 
sion-lenses and the condenser. 
Instruments, Microtome.—The instruments for fine 
dissection are those commonly used in histology. In 
addition, needles of glass and platinum are necessary, 
and thin spatulas of nickel to convey the sections, ete. 
The ordinary razor, which serves for hand sections, 
will not do for the thin, wide sections necessary for 
the discovery of bacteria. In this case a microtome 
must be used, an instrument for making thin sections, 
for which purpose those of Thoma or Vérick are the 
best. Sometimes the object’ to be examined is 
hardened by freezing it with ether spray, since this 
makes it possible to cut thin sections by hand. This 
is Jung’s process. 
Non- staining Liquid Reagents. — Acids, bases, 
alcohol, oil of aniline, and other essences serve to 
