MICROTECHNICAL METHODS 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 203 
W. J. G. Lanp 
An improved method of replacing the paraffin solvent 
with par 
In paraffin imbedding the almost universal custom when repla- 
cing a paraffin solvent with paraftin is to add from time to time small 
pieces of. paraffin to the solvent, until at room temperature no more 
paraffin is dissolved. Then the container is either placed in a low 
temperature oven or on an oven of higher temperature and paraffin 
added until the new saturation point is reached. The container is 
then placed in an oven having a temperature one or two degrees 
above the melting point of the paraffin and more paraffin is added. 
When the last paraffin has melted the mixture is poured off and 
replaced with pure melted paraffin. The object in repeatedly add- 
ing small quantities of paraffin is to prevent a too rapid increase in 
the eee of the xylol-paraffin or whatever solvent is used for 
paraffin. 
Objects to be imbedded, being heavier than xylol, sink to the 
bottom. Paraffin, which is heavier than xylol, also sinks, with the 
result that the objects are almost immediately surrounded by a 
dense layer of dissolved paraffin, thereby defeating the end sought 
by a gradual addition of paraffin. It has repeatedly come to the 
_ hotice of the writer that much of the damage to delicate plant tissues 
takes place during the replacement of the solvent by paraffin. 
Many otherwise careful workers are particularly careless at this 
point. 
In order to prevent the object from coming into jacandinte con- 
tact with the dense xylol-paraftin solution, a piece of wire gauze is 
bent in such a manner that it forms a support 2-3 cm. above the 
object, and xylol sufficient to rise 1-2 mm. above the support is 
added. The container (a shell or bottle) is then filled with blocks 
397] {Botanical Gazette, vol. 59 
