784 PEESEEVATION OF OBJECTS. 



cambric. Among the cements used for vegetable objects are the fol- 

 lowing : — -Asphalte, japanner's gold size, black japan sealing-wax 

 varnish, Eobinson's liquid glue, gum mastic and caoutchouc dissolved 

 in chloroform. Objects are put up (i.e. preserved) either as dry or as 

 wet objects. For dry objects, the oUs and the Canada balsam are the 

 preservative materials, but they are not suited for wet objects. Before 

 mounting objects in Canada balsam they must be perfectly clean and 

 free from moisture. The moisture is got rid of by immersing them in 

 rectified spirit for an hour or so ; the spirit is then removed by placing 

 the tissue for a few minutes in turpentine or oil of cloves in a watch- 

 glass or on a slide. Both of these agents, owing to their high re- 

 fractive index, render tissues transparent. In this respect clove oil is 

 more powerful than the turpentine, and therefore it is preferred when 

 great transparency is desirable. When the tissue is sufficiently clari- 

 fied, a drop of Canada balsam solution is placed on a slide, the tissue 

 is transferred to it, the cover-glass applied and gently pressed down 

 in order to flatten the tissue. The balsam soon dries, so that the 

 cover-glass is permanently fixed. The solution of Canada balsam is 

 thus prepared : — Place the ordinary kind obtained from the shops in a 

 saucer, cover it with blotting-paper to protect it from dust, place it 

 near the fire for some days, untU the balsam is so dry that it becomes 

 as hard as ice when it cools. Dissolve this perfectly dried bakam in 

 chloroform, or turpentine, or benzole (the latter is to be preferred), 

 and keep it in a corked bottle. The solution ought to be as thin as 

 milk. The mounting of objects in this solution of dried balsam has 

 quite superseded the old method of mounting objects in undried 

 balsam with the aid of heat. The solution of chloride of calcium is 

 adapted for the preservation of wood and leaves, and for most kinds of 

 isolated tissue. The colouring matter in the cells, however, is always 

 more or less altered by it, while grains of starch, if present, swell up 

 and can scarcely be recognised. The strength of the solution is ope 

 part of lime to three of water. Glycerine is used in equal parts 

 mixed with camphor water, which prevents the tendency to mUdew. 

 The chlorophyll and the grains of starch remain unchanged, and the 

 laminae of the starch appear more beautifid after a few hours' immer- 

 sion in the glycerine solution. Canada balsam and copal varnish are 

 used for the preservation of dry and fossil woods. Thin se'ctions 

 should be made, and treated as above directed. If the entire structure 

 of any exogenous wood is required to be examined, the sections must 

 be made both in the transverse or horizontal, and in the longitudinal 

 or vertical direction. The vertical section, made parallel to the 

 medullary rays, or, in other words, along the course of them, shows 

 the nature of these cellular rays, which proceed horizontally from the 

 centre, enclosed between the layers of woody fibres, and which are 

 known to the cabinetmaker as the silver grain of the wood. In coni- 



