THE Microscope. 175 
thoroughly washed off with pure water, and the water removed 
with blotting paper. 
One of the most common mediums used for fluid mounts 
is slightly acidulated dilute glycerine; this consists of an equal 
mixture of glycerine and water, to an ounce of which a very 
few drops of acetic acid are added. 
To mount in glycerine jelly it is necessary to melt the jelly 
in a water-bath. Care should be taken that the jelly is heated 
only just enough to melt it, any extra heat being prejudical. 
A drop of the melted jelly is placed on a warm slide with a 
glass rod. On this drop the section or tissue is placed, and an- 
other drop of the jelly placed over it. The cover is lowered 
upon it and pressed down against the slide more or less firmly, 
according to the nature of the tissue. When cold, the excess 
of jelly is easily removed with a knife. It is a good plan to 
run a ring of zinc around the edge of the jelly as otherwise it 
is liable to dry and crack. Delicate sections that are easily 
injured by pressure should not be mounted in this medium, 
while such tissues as yellow elastic tissue show unusually well 
in it. 
Mounting in balsam is an easy and quick method. Balsam, 
as a mounting medium, includes any balsam that has been dis- 
solved in any fluid, as balsam and benzole, balsam and chloro- 
form, balsam and absolute alcohol, dammar, ete. 
To mount in balsam, the stained tissue is dehydrated by 
allowing it to remain in absolute alcohol for a few minutes; it 
is then transferred to the oil of cloves, until it is rendered quite 
transparent; from the oil it is transferred to the center of the 
glass slide and a drop of balsam placed over it. Then the cover 
is applied. 
If it is desired to finish these slides with a layer of the 
zine cement, it will be necessary to place some medium over 
the balsam to keep it from mixing with the zinc. This is eas- 
ily and effectually accomplished by placing around the edge of 
the mount a thin layer of colorless marine glue; just enough to 
coat the exposed balsam. This dries very quickly ; when dry 
a thin layer of the white zinc is put on and the mount laid 
aside for a few days. The second coat of zine will finish the 
slide in good shape. The colorless marine glue is dissolved in 
