208 BOTANICAL GAZETTE [SEPTEMBER 
gelatin hardens. The plates should be sufficiently close so that the 
specimen will be held in place by friction against the glass while the 
gelatin is hardening. The amount of space required for different 
specimens is easily regulated by the thickness of the glass separating 
the plates. Modifications of this method can easily be made to meet 
the requirements of the material. The formalated gelatin hardens in 
a few hours, but it is best to allow the preparation to remain open at 
the top from twelve to twenty-four hours, filling in more gelatin if 
necessary. Finally, when the top has hardened and dried down about 
one-fourth of an inch, the space left should be carefully cleaned out 
and filled in with hot, hard balsam, which should make the seal per- 
fectly air-tight. After this the mount should be cleaned, bound with 
lantern slide binders, and labeled. 
The formula for the glycerin gelatin used is 20 parts of best quality 
French or other clear gelatin, to parts glycerin, and 100 parts water. 
Steam the mixture until the gelatin is melted, then cool down to 55° 
C., and add the white of one egg to about every 200%. After this is 
thoroughly incorporated steam again for about thirty minutes, or until 
the egg albumen is thoroughly cooked and white. Stir occasionally 
during this last steaming to insure complete coagulation of the egg. 
Now add malic or some similar acid to make the mixture neutral or 
slightly acid to litmus, and after carefully incorporating this strain 
while hot through cloth, and then filter through paper. In case it is 
desired to keep any of the glycerin gelatin in stock add, before filter- 
ing, one part salicylate of soda to each roo parts of the mixture, or 
else keep the stock flask sterile by occasional steaming. I use the 
latter method. 
As before mentioned, the formalin is not added to the stock gela- 
tin, but to what is used in making each preparation at the time of fill- 
ing or imbedding. When once the gelatin is hardened by formalin it 
is insoluble in water and cannot be melted even at boiling tempera- 
ture. The formalin, of course, also makes it antiseptic. If the formalin 
is permitted to evaporate from the gelatin the latter may again become 
fluid. 
Other formulas for glycerin gelatin may be used instead of the one 
described. Some prefer to use a larger quantity of glycerol and less 
water, which has an advantage, in that the mixture so prepared is less 
liable to dry out. 
In conclusion the writer wishes to disclaim any originality in the 
