190 The American Naturalist. [March. 
lated alcohol (50%, with a little hydrochloric acid) ^^ min- 
ute, then placed in alcohol containing a few drops of ammonia. 
Connective tissue and nerves are unstained, while ganglion 
cells are stained deep blue. 
The last two methods of staining may be followed by picric 
acid, which stains the uncolored elements yellow. The process 
is as follows : 
After the sections have been fixed to the slide with collodion 
and the parafRne dissolved with turpentine or zylol, the slide 
is placed in turpentine containing a few drops of a solution of 
picric acid in absolute alcohol. In a few seconds, nerve-fibres, 
connective tissue, and muscles are stained yellow. The slide 
is next to be placed in turpentine containing a few drops of al- 
cohol, to wash away the excess of picric acid, then in pure 
turpentine or xylol preparatory to mounting in balsam. 
Zylol Dammar.'— M. Martinotti advocates the use of 
dammar dissolved in zylol as a mounting medium, to be pre- 
ferred to balsam in certain cases. He prepares his solution in 
the following way : 
Forty grams of dammar and forty grains of zylol are mixed 
together in a stoppered bottle and allowed to stand for three 
or four days at the ordinary temperature ; the solution is then 
filtered. The filtrate, which will amount to about 70 grams, is 
then evaporated in a water-bath down to about 45 grams. 
The object of this concentration is to obtain a solution of the 
resin in the smallest quantity of zylol possible, just enough in 
fact to merely dissolve the resin. This concentrated solution 
becomes yellow, but retains its limpidity. The next step is to 
dilute this solution with oil of turpentine, by which means the 
yellowish color is made to almost disappear. 
