THE GLYCERIN METHOD 
99 
Eosin is a good stain for many algae and fungi, when sharp out¬ 
lines rather than cell contents are to be brought out. After the 
material has been fixed and washed in water, stain in an aqueous 
solution of eosin for 12 to 24 hours. Pour off the eosin, which can be 
used repeatedly, and pour on a 1 or 2 per cent solution of acetic acid 
in water. Pour this off and pour on some more of the acid, until 
very little stain washes out. The process may require 2 to 5 minutes. 
Then place in 10 per cent glycerin containing about \ per cent acetic 
acid, and allow the glycerin to concentrate. The acetic acid is to 
prevent the stain from washing out. When the glycerin has reached 
the proper concentration, mount and seal as before. 
The following is a rapid method for forms like Eurotium and 
Penicillium: Fix in 100 per cent alcohol about 2 minutes; stain in 
aqueous eosin 5 minutes; wash in water about 1 minute; fix in 
1 per cent acetic acid 1 minute; then mount directly in 50 per cent 
glycerin to which about 1 per cent acetic acid has been added. It is 
hardly worth while to try this method with forms which have large 
cells; they are almost sure to collapse. If a form like Eurotium passes 
through the earlier processes without danger, but collapses when 
put into the 50 per cent glycerin, put it into the 10 per cent glycerin 
and allow the glycerin to concentrate. 
Mounting without Fixing or Staining.—Lt is sometimes desirable to 
retain the natural color of an obj ect. The chlorophyll green can usually 
be preserved by mounting directly in glycerin without any previous 
fixing. Other colors also are often preserved in this way. Moss 
protonema makes beautiful preparations by this method. If possible, 
select protonema showing the very young moss plants. The brown pro¬ 
tonema and brown bulbils preserve their color perfectly. Wash the dirt 
away from the protonema, which is then placed in 50 per cent glycerin. 
The brown or black spores of fungi are readily mounted in this way. 
The method is very useful when one finds a single specimen 
of Pediastrum , or any small form which would be lost in the more 
complicated processes. Place a large drop of 10 per cent glycerin 
on a slide; with a pipette, transfer the object to the drop, and allow 
the glycerin to concentrate. Then add a cover and seal the mount. 
GLYCERIN JELLY 
It is almost never necessary to mount anything in glycerin, because 
material can be transferred directly from glycerin to glycerin jelly. 
