416 APPENDIX. 



tissues at a temperature whose variations are included within the 

 limits of 50 to 52 C. 



The tissue must remain in the melted paraffin until every portion 

 of it has been completely filled with the embedding mass and all the 

 chloroform has been driven off. This latter point is a matter of 

 importance in insuring the proper consistence of the paraffin for satis- 

 factory cutting, since when the paraffin contains traces of chloroform 

 it is too soft and friable to yield the best results. In order to deter- 

 mine whether all the chloroform has been driven off, a clean thin iron 

 rod is heated and plunged into the melted paraffin, care being taken 

 that the rod is not too hot when immersed, lest the tissue be over- 

 heated. So long as traces of chloroform are present, bubbles follow 

 the introduction of the heated rod ; when bubbles no longer appear, 

 all the chloroform has been driven off. 



After the complete dissipation of the chloroform, the tissue is trans- 

 ferred for a few minutes to a second capsule containing fresh, unused, 

 melted paraffin of such consistence as is best adapted to sectioning 

 under the conditions of season and particular object in view ; the 

 quantity of melted paraffin should amply suffice to fill the mould 

 which is to be employed in the next manipulation. 



f. Embedding the Tissue. For this purpose some form of mould 

 must be devised, which may be the simple paper box, made by fold- 

 ing over a block the sides and ends of a piece of sized paper some 

 4 cm. wide by 8 cm. long ; more convenient are the adjustable metallic 

 embedding frames furnished by dealers, those made by Jung, of 

 Heidelberg, and sold by various firms in this country, being par- 

 ticularly serviceable. When the paper box is used, it should be fixed 

 to a loaded cork before the paraffin is poured into it; when the metallic 

 frame, it must closely rest upon a piece of polished glass. In either 

 case, the mould is placed in a broad dish, whose depth somewhat 

 exceeds the height of the sides of the mould when resting in position 

 for use. 



The mould and dish being ready, the capsule containing the fresh 

 paraffin and specimen is removed from the oven, and the paraffin 

 poured at once into the mould, which should be completely filled ; 

 after this has been done, the tissue is seized lightly with the slightly- 

 warmed forceps, and rapidly transferred to the mould ; a warm needle 

 should be at hand with which to arrange the tissue, so that the pro- 

 posed plane of section shall lie parallel to one of the smaller ends of 

 the mould, while its principal axis corresponds with the bottom upon 

 which the tissue rests. 



As soon as the specimen is properly placed and this is often a 

 matter of great consequence steps should be taken to harden the 

 paraffin as rapidly as possible. To this end, the dish supporting the 



