PARAFFIN-INFILTRATION. [19 
kept at 59° C., and the material is subjected to this temperature only long enough 
to secure proper infiltration. Generally a few hours are sufficient. A small oven 
used for this purpose is shown in fig. 105. For large laboratories or classes of 
students the separate-compartment paraffin oven designed by Dr. Lillie is very 
convenient. Griibler’s paraffin is preferred, and for the climate of Washington we 
use mixtures of three grades of hardness, viz, melting point 52° C., 58° C., and 
60° C., increasing ot decreasing the amount of the harder sorts according to the 
time of year.’ Dirty pene should never be used. All the stock paraffin should 
be carefully protected from dust. ‘The same 
remark applies still more pertinently to the 
sections cut on the microtome. They should 
be made in still air, in a clean room, and should 
be carefully protected from dust until stained 
and mounted. The paraffin -infiltration is 
usually a simple process unless the material 
contains air. The embedded material is given a 
serial number which is scratched on the paraffin 
(fig. 106), until it is fastened to the cutting 
block, when it is written on the latter (fig. 
107). ‘These blocks are kept as shown in fig. 
108. ‘The sections are fastened to clean slides 
by a very thin layer of Mayer’s egg albumen 
fixative (see Lee’s Vade Mecum, 5th ed., p. 143), or with pure water, or preferably 
with 0.5 per cent gelatin water (which will not keep untreated, but may be preserved 
by adding 3 per cent phenol); the paraffin is removed (after cautious melting) by 
exposure to turpentine or xylol, alcohol is then substituted, and thereafter graded 
mixtures of alcohol and water down to alcohol containing 50 or 60 per cent of 
water, followed by the stain. Water is then removed by passing through graded 
alcohols into absolute alcohol; xylol or bergamot oil is substituted for the alcohol, 
and the section is finally mounted in balsam. Coplin’s staining jar is preferred 
(figs. 109, 110). A series of staining jars, ready for 
use, is shown in fig. 111. The section properly fast- 
ened to the slide, and dry, is started in at the left after 
melting the paraffin with gentle heat, and is taken out 
at the right ready for mounting in balsam.{ In this 
series of jars the gradations are as follows, beginning Fig. 107.4 
Fig. 106.* 
*Fic, 106.—Infiltrated tissues embedded in paraffin in a watch-glass and now ready to cut out 
and mount on blocks for the machine. 
+Fic. 107.—Infiltrated material embedded in paraffin and mounted on a pine block ready to cut 
on the microtome. Actual size. 
{Sections designed for photo-micrographic work must not only be cut in clean air, but mounted 
in absolutely clean balsam. So much trouble has been experienced in finding such dissolved bal- 
sam on the market that the writer now makes his own. The dry balsam is heated in an oven until 
all easily volatile products are driven off and it becomes brittle. It is then dissolved in xylol and 
filtered under a bell jar to exclude dust. The filtering usually requires several days. 
