PARAFFIN-INFILTRATION. 



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 or decreasing the amount of the harder sorts according to the 

 time of year. Dirty paraffin 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. 

 1 08. 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, no). A series of staining jars, ready for 

 use, is shown in fig. in. 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.t In this 

 series of jars the gradations are as follows, beginning 



*Fic. 106. Infiltrated tissues embedded in paraffin in a watch-glass and now ready to cut out 

 and mount on blocks for the machine. 



fFic. 107. Infiltrated material embedded in paraffin and mounted on a pine block ready to cut 

 on the microtome. Actual size. 



J 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. 



