151 



The quantity of water contained in the above mixture is not abso- 

 lute, for in some cases it will be necessary that the medium should 

 contain a greater quantity than in others. For example, if it is 

 required that the medium should penetrate into all the pores of an 

 object, with the view of increasing its transparency, the medium 

 must be more diluted. If, on the other hand, it is desirable that 

 objects should contain vacuities, as the tracheal system of insects, the 

 jelly, when cold, must be sufficiently stiff to prevent its being drawn 

 into the tubes, when the water contained in them, or that which has 

 been made to fill them, has left them to combine with the medium 

 during its evaporation. 



Not any of the above ingredients are at all likely to injure any 

 objects mounted in the medium. The gelatine has no injurious ten- 

 dency on either animal or vegetable structures ; and honey is 

 remarkable for its preservative properties, as it is well known that 

 leaves, flowers, and fruit may be kept in it for a great length of time 

 without losing their sensible properties to any material extent. The 

 alcohol is added as a solvent of the kreosote, and for diffusing the 

 latter more perfectly through the jelly, and to assist in its preserva- 

 tion, as well as the objects mounted in it ; also to defend it from the 

 attacks of mould, insects, &c, for to the latter the compound would 

 be too palatable without some such addition. 



This medium is chiefly intended to be used in the same way as 

 Canada balsam, viz., without cells ; but in cases where they must be 

 made use of, the cover should not be laid on the cell in the usual 

 way, but be made to fit into it, so that as the medium contracts by 

 evaporation the cover may descend bodily; no cementing of any 

 kind is required ; and as it is a matter of indifference about the cells 

 being tight, they may be formed of any porous material, such as 

 cork, pasteboard, &c* 



In mounting objects the usual way, without cells, the chief and 

 most important point to be attended to is to avoid enclosing any air- 

 bubbles ; and if the object is dry, such as a section of wood, it should 

 be soaked, or even boiled, for a short time in water, which will drive 

 all the air out of the pores ; it is then placed on a piece of paper, in 

 order to drain off the superfluous moisture ; and, the medium having 

 been melted, either by placing the bottle in warm water or over a 



* Since writing the above, I have found it desirable in most instances to cover the 

 exposed edge of the mounting medium with a little varnish of some kind, to prevent 

 the consequences attending its contraction, which invariably takes place to some 

 extent. 



