ZOOLOGY AND BOTANY, MIOROSCOPY, ETC. 
413 
Upon this layer the sections are arranged. Directly this is done the 
slide is gently heated over a Bunsen’s burner in order to soften, but not 
to melt, the paraffin imbedding. Any excess of fixative may now be 
removed by merely draining it off. The fixative is now to be thoroughly 
dried, and as this requires several hours, the slides should be covered 
over with a bell-jar and left till next day. The paraffin is then dissolved 
out either with warm turpentine or with chloroform, and then the solvent 
extracted by running some strong spirit over the slide. If the prepara- 
tions have been stained en masse the slide is then dehydrated in alcohol, 
cleared up with oil of cloves, aud mounted in balsam. If the sections 
require to be stained, the slide is merely placed in the staining solution, 
and when withdrawn, rinsed with spirit, after which it is mounted in 
balsam. As indicated above, almost any reagent may be used, provided 
it be not purely aqueous. 
Use of Cajeput Oil for dissolving Canada Balsam.* — Prof. 0. 
Beccari recommends the use of cajeput oil, obtained from Melaleuca 
Leucodendron, instead of oil of cloves, for dissolving Canada balsam. It 
has the advantage of being soluble in dilute alcohol, and the object can 
therefore be transferred directly from the dilute alcohol to the oil, which 
is not the case with oil of cloves. In addition, objects placed in cajeput 
oil and alcohol take up methyl-green and retain it in Canada balsam. 
New Method of finishing Balsam Mounts.! — Mr. F. N. Pease re- 
marks: — “ It is only a question of time, when balsam mounts thoroughly 
hardened and unprotected from atmospheric influence will be ruined, on 
account of the cover-glass becoming detached, especially during rough 
handling. Discoloration of the mounting medium often occurs previous 
to the more serious result above mentioned, proceeding from the margin 
inward. On the other hand, preparations in which the balsam, storax, 
or other resinous media are used, are often injured by the running in of 
the cement used for finishing the slide, when sufficient care is not taken. 
A method has been adopted, which effectively obviates these objections, 
and at the same time renders it possible to mount and finish a slide at 
once, without the delay due to allowing successive coats of cement to 
dry before others are applied. The mounts need not be thoroughly 
hardened before finishing, provided the nature of the preparation does 
not require it. 
The method used is as follows : — The object is mounted on the slide, 
applying the cover-glass in the ordinary manner, using either balsam, 
hardened balsam, balsam and benzol, storax, or dammar. The slide is 
then heated to drive off the solvent, or more volatile constituents, either 
gently in the water-bath or at a higher heat, even boiling carefully over 
a spirit-lamp when the nature of the object will permit. 
When cold, the superfluous mounting medium, when present, is care- 
fully removed, then a narrow ring of paraffin wax is applied in the 
following manner : — hard white paraffin wax (such as is used for imbed- 
ding) is heated in a suitable capsule until it is melted and quite limpid. 
With the aid of a very small camel’s hair pencil, the melted paraffin is 
applied at the edge of the cover-glass, covering the exposed mounting 
medium and instantly solidifying. With round cover-glasses and a 
turntable, very neat narrow rings of paraffin wax can be readily and 
Malpigliia, iii. (1890) p. 410. 
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