APPENDIX. 129 



agents used in the reduction of those hard osseous-like 

 tissues. A perfect section should have but one layer of cells, 

 which may be admirably seen when mounted in a cell with 

 weak spirit. 



SECTIONS OP WOOD (plate 3, figures 54 to 59). To make 

 thin .sections of hard wood it will be necessary to employ 

 some kind of cutting machine. There are several of these, 

 more or less expensive, but the principle of construction in 

 all is similar. The wood, after some preparation, and being 

 cut to the requisite length, is driven by a mallet into a brass 

 cylinder, at the bottom of which works a fine screw with a 

 milled head. The wood is pushed to the surface of the tube, 

 and to any degree above it by the revolution of the screw ; 

 when a sharp knife, ground flat on one side, is brought with a 

 sliding motion in contact with it. The slices may be removed 

 from the knife by a wetted camel-hair pencil, placed in some 

 weak spirit, and examined at leisure ; the thinnest and most 

 perfect section being retained for mounting. Green wood 

 previous to being cut should be placed in alcohol and after- 

 wards in water. Hard and dry wood may be made suffi- 

 ciently soft for slicing by first immersing it in water for some 

 days. Sections of the above may be mounted either in 

 balsam or fluids. Stems of plants, horny tissues, and many 

 other substances not sufficiently hard to be ground down, 

 may be cut into slices of extreme thinness by this handy 

 instrument. In order to obtain a correct idea of the struc- 

 ture of wood, bone, and shell, sections should be made in 

 vertical, transverse, and oblique directions. 



CUTICLE OP PLANTS (plate 2, figures 42 to 46), HAIRS 

 (plate 3, figures 74 to 88), AND SPIRAL VESSELS (plate 2, 

 figures 47 to 49), may all be obtained by macerating the 

 leaves and stems of plants in water, and afterwards dissect- 

 ing them with the needles. Good specimens of the cuticle, 

 showing the stomata, may be often obtained by simply 

 peeling off the skin with a sharp knife. Hairs may be de- 

 tached from various parts of a plant by a similar process. 

 Spiral vessels will, however, require to be separated by the 

 needles from the surrounding tissues. All delicate vegetable 

 preparations arebest displayed when mounted in a cell with 

 weak spirit. 



Cells for mounting objects in fluid are generally formed 

 of some kind of varnish upon which the fluid will not act : 

 gold-size and Brunswick black are most commonly used. 

 To form a cell, simply charge a camel-hair brubh with the 

 varnish, and enclose with a broad black ring a small circular 

 space on the centre of the slide. When quite dry, it is ready 

 ft 



