82 Tue Microscope. 
Specimens should be allowed to remain in the fluid at least 
two weeks, during which time they should be removed to fresh 
solutions three or four times, after which it is not necessary to 
disturb them. 
At the end of the two weeks, or after a longer time if de- 
sired, the tissue is well washed in distilled water until no more 
color comes from it. It is then transferred to some hardening 
fluid of greater power, usually alcohol. The alcohol should be 
quite dilute for the first two or three days; then common alco- 
hol takes its place for the next two or three days, when absolute 
aleohol completes the hardening in from two to three days 
more, the time depending upon the size of the specimen, the 
nature of the tissue and other factors. This is the most satis- 
factory of all the general methods of hardening. It insures 
even shrinking and hardening and leaves the tissue in good 
condition for cutting and staining, and besides there is not the 
danger of injuring the specimens that accompanies the harden- 
ing process of some regents. 
MULLER’S FLUID AND ALCOHOL. 
Muller's uid. eee 3 parts. 
PAC ONO) o> = eee ee 1 part. 
This mixture is used especially for the brain, spinal cord, 
and retina. After frequent changes as described above, the 
hardening is completed in alcohol. 
It should be made only as required and should be kept in a 
dark place. 
MULLER’S FLUID AND NINETY—FIVE PER CENT. ALCOHOL. 
Dr. Seiler recommends a solution composed of equal parts 
of these regents, claiming that large organs, as whole kidneys, 
brains, etc., may be hardened throughout in a comparatively 
short time. 
ALCOHOL. 
Alcohol is very generally used to commence and complete 
the hardening of tissues. The pieces of tissue should be quite 
small or the whole organ must be injected with the alcohol. It 
is better to commence with dilute solutions and complete the 
process in the strongest spirit. 
