Bearer eR ARTICLES 
AN IMBEDDING MEDIUM FOR BRITTLE OR WOODY 
TISSUES 
A mixture of rubber and paraffin as an imbedding medium for 
brittle objects was first described by J. B. Jounston,’ and the following 
is a modification of his original formula. 
-Melt 98 grams of paraffin of the melting point usually used, to it 
add 0.4 gram of asphalt (mineral rubber) and heat until the asphalt is 
dissolved, giving the paraffin a dark color. The purpose of the asphalt 
is to increase the power of the paraffin to dissolve rubber. For very 
woody tissue so much asphalt may be added that the paraffin becomes 
black. To the dark-colored liquid paraffin add 2 grams of crude rubber 
cut into very small pieces, and keep the mixture at a temperature of 
95° C. for several hours, or at the melting point of the paraffin for several 
days until the solution is saturated with rubber. Then decant the 
clear supernatant liquid and allow it to cool. Use the dark solid exactly 
as paraffin is used. 
There are two points which require care in manipulation. First, 
as the rubber tends to separate out slowly if the mixture remains in the 
melted condition too long, allow the mixture to cool when not infiltrating; 
second, the elasticity of the mixture leads to the formation of internal 
air bubbles if the “blocks” containing the imbedded object are cooled 
too rapidly. During winter, when the water is very cold, it is best 
not to immerse the blocks completely, but simply let them rest on the 
surface until hard. The addition of the rubber decreases the melting 
point of the mixture by two or three degrees. 
The relative amounts of the different components of the mixture can 
be modified to suit individual requirements, and with a little practice 
the results obtained equal those obtained with the much more cumber- 
some celloidin method.—H. M. Benepict, University of Cincinnati. 
t Journ. Micr. and Lab. Methods 6: 2662. 1903. 
Botanical Gazette, vol. 52] [232 
