1897 ] BRIEFER ARTICLES 207 
cells before the chlorophyll escapes or breaks down. In order to 
accomplish this, the air on the surface, and as far as possible in the 
intercellular spaces of the tissues to be treated, must either be removed 
by immersion in 90 to gs per cent. alcohol for fifteen or twenty min- 
utes, according to the size and penetrative resistance of the specimen, 
or else be freed by placing in water and removing the air with an air 
pump. Soaking for some time in boiled water after the latter has 
cooled is also effective. Good results may be obtained by combining 
all these methods. When the tissues are reasonably free from air the 
specimens should be placed in a dilute (5 per cent.) glycerol solution 
containing enough dissolved copper sulphate or copper acetate to give 
it a marked bluish tint. The solution should be boiled before using 
to free it from air. At the time of using, enough formalin should be 
added to make the solution about 1 per cent. The specimens should 
be left in this until all of the green parts have been penetrated by 
the copper and have assumed a bluish green color. They should then 
be removed to a dilute glycerin-formalin solution free from copper. 
This will gradually dissolve all the copper not in combination with 
chlorophyll and thus bring out the natural shades and variations. 
After thorough washing and clearing in this latter solution the mate- 
tial may be preserved, without change, in glycerin-formalin solution 
Or any of the common media except strong alcohol. 
For class use and exhibition purposes the specimens are best 
mounted in glycerin gelatin. Flat specimen jars with parallel sides 
and clear glass may be used, or in many cases better results may be 
obtained by mounting the specimens between glass plates of sufficient 
Size. Old negative plates are good for this purpose. These are made 
into mounting chambers by cementing narrow strips of glass between 
the two sides and one end, the other end being left open. The most 
Satisfactory cement found for this purpose is Canada balsam, boiled 
until when cool it will be hard but not brittle. Before the cell is 
made the glass should be thoroughly cleaned, as it is difficult to clean 
the inner walls afterwards. 
When the cell is prepared the material is shoved in between the 
plates and arranged as desired. Two per cent. formalin is then added 
to the warm glycerin gelatin and this is poured in at one side to the 
bottom, from which it rises and surrounds the specimens. Any bub- 
bles adhering to the specimens may be disengaged with a knitting 
needle or a fine, stiff wire, and the material finally arranged before the 
