THE PARAFFIN METHOD 
113 
(or several days, if time permits) at room temperature, place the shell 
on a pasteboard box—slide boxes are good—on top of the paraffin 
bath. Do not place the shell directly upon the metal of the bath, 
since it is better to minimize heat. As soon as the paraffin is dis¬ 
solved, add some more, this time leaving the cork out, in order that 
the xylol may evaporate. About 24 hours on the top of the bath 
should be sufficient. 
THE PARAFFIN BATH 
This step is usually called infiltration, but when the transfer 
from the clearing fluid to paraffin is made gradually, as has just been 
indicated, the process of infiltration is already begun. It is now 
necessary to get rid of the xylol or other clearing agent. This is 
accomplished, to a considerable extent, by pouring off the mixture of 
xylol and paraffin and replacing it with pure melted paraffin. Pour 
off the pure paraffin immediately. This is important. You will 
notice that often, when the pure paraffin is poured on, a froth or 
scum will appear on the surface. Much of the xylol will be in this 
scum, and, if allowed to remain, it would diffuse into the mass and 
greatly prolong the time needed for infiltration. So, pour it off and 
add more pure paraffin, for some xylol remains in the tissues and must 
be removed. Do not put the shell into the bath, but use a flat dish of 
some sort. The main object is to have a fairly large surface exposed, 
so that the remaining xylol may evaporate as rapidly as possible. 
Change the paraffin 2 or 3 times. Soft paraffin (about 45° C.) may 
be used at first, but the second should be the paraffin of the grade in 
which the material is to be imbedded. If there are two baths, one 
should be kept at 46° C. and the other at 52° C., if the material is to 
be imbedded in 52° C. paraffin. While using the soft paraffin, keep the 
material in the 46° C. bath; for the harder paraffin, use the 52° C. bath. 
If there is only one bath, there is no object in using the 45° C. paraffin. 
Do not throw away the paraffin which you pour off, but put it in a 
waste jar or beaker, or, still better, in a small tin lard pail, in which 
you have made a lip to facilitate pouring. This can be placed in the 
bath, or, in winter, on the radiator, and the xylol will gradually 
evaporate. After long heating, the paraffin not only becomes as 
good as new, but even better, since it becomes more homogeneous 
and tenacious. If it contains dust or debris of any kind, it may be 
filtered with a hot filter. 
