PREPARATION, MOUNTING, AND COLLECTION OF OBJECTS. 195 



sufficiently for the gradual penetration of the liquid to their interior. 

 The entire mass being then exposed to the air, the slow evaporation of 

 its water will at last reduce it to a consistence sufficiently firm to enable 

 sections of it to be taken; or the water may be drawn out by steeping in 

 Alcohol. This plan has been found to answer for the entire bodies of 

 Insects, Stems of herbaceous Plants, and the like. But when the sec- 

 tions are to be cut of the extreme thinness required for showing minute 

 histological detail, it is much better to use either Paraffine slightly soft- 

 ened with lard, or Cacao-butter, which last has been much recommended 

 for the imbedding of structures of extreme delicacy. The material to be 

 cut must be first dehydrated, or deprived of its Water; which is done by 

 letting it lie fora time in ordinary Spirit, then transferring it to Recti- 

 fied spirit, and at last treating it with absolute Alcohol. From this it is 

 to be transferred to some volatile oil; oil of bergamot being used for 

 delicate objects; oil of turpentine answering sufficiently well for larger 

 bodies. When this has completely replaced the spirit, the body is to be 

 immersed for some little time in a hot saturated solution of paraffine in 

 oil of turpentine. When it has lain sufficiently long in this to be thor- 

 oughly penetrated, it is to be immersed in the melted paraffine, which 

 should not be more heated than is necessary to keep it quite liquid; and 

 it should be moved about in this for some little time, an occasional gentle 

 squeeze being given to it with the forceps, so that the solution may be 

 replaced as completely as possible by the liquefied paraffine. When 

 hardened by cooling, the substance thus prepared may be ' imbedded ' in 

 any ordinary cylinder Microtome, in the manner already described; the 

 coating with gum being of course omitted. But if the sections are to be 

 made either with the Rivet-Leiser Microtome, or by hand, it is necessary 

 to provide a mould into which the imbedding- material can be poured. 

 This may be made of cylindrical form, by twisting a strip of paper round 

 the end of a small ruler; or a brick-shaped block may be cast in a mould 

 made by turning up the edges of a suitably-sized piece of paper, and 

 pinning together the cross-folds at the two ends. But it is generally 

 more convenient to use for this purpose small boxes of tin 2 inches long, 

 and 3-4ths of an inch in breadth and depth, with removable bottoms. A 

 small piece of filtering paper being placed between the bottom and the 

 sides of the box, and the substance to be imbedded being held in it in the 

 most suitable position, the paraffine is poured in until the box is 

 completely filled, and this is set aside to cool. When the paraffine has 

 perfectly solidified, the box it to be lifted off its bottom; and the block, 

 being pushed out of it, is then ready for cutting. In using the section- 

 knife, care should be taken to keep it constantly wetted with methylated 

 spirit; and it is desirable that each section should be removed from 

 it before another is taken. When, for the study of the anatomy of an 

 animal, sections are being taken in series, and it is important that their 

 order should be preserved, a set of watch-glasses should be previously 

 provided, each about half filled with spirit, and the sections successively 

 taken should be dropped singly into them; care being taken in the 

 arrangement of the glasses to maintain the relative position of the 

 sections. In order to dissolve out the imbedding material, the sections 

 should be soaked in oil of turpentine with about one-fourth part of 

 creasote; and if its structure is suitable for examination with high powers, 

 it may be cleared by a short immersion in oil of cloves. They are then 

 to be mounted either in Canada balsam solution ( 209) or in Dammar 

 cement. 



