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Journal of the 
has all the appearance of an air-bubble, and which may either take 
a globular form or expand till it completely fills the cell. In the 
former case it is evident that the balsam is finding its way into 
the cell, though slowly, and if it is thin enough to retain its soft 
condition for a few days, the bubbles will probably disappear; but 
when they completely fill the cell it is a sign that the balsam 
cannot find entrance, and the object can then only be cleared by 
again soaking it in the fluid solvent. Among the objects most 
liable to this inconvenience may be mentioned sections of some 
woods, also such Bryozoa as some of the common Catenicellce , the 
avicularian processes of which usually contain perfectly closed-in 
chambers. In the closed gonotlieca) of some of the most delicate 
Hydroids the same cause is followed by different results—the 
escape of the fluid and the inability of the balsam to enter, 
causing the collapse of the thin chitinous investment, instead of the 
formation of a vacuum-bubble, as is the case where the wall of the 
closed cavity is strong enough to resist the pressure of the balsam. 
Precisely the same phenomenon is observed when delicate vegetable 
tissues are placed in glycerine, and the means used to prevent 
it, viz. thickening the medium very gradually, suggested to me the 
idea of applying the same principle to balsam mounts. An easy 
method of doing this is to place the object in turpentine on the slide 
under a large cover-glass, and with a glass rod, deposit round the 
margin an embankment of soft balsam, then lay the slide aside till 
the balsam and turpentine are thoroughly mixed, which will be a 
slow and gradual process. It is not advisable to use carbolic acid for 
this work, at least if there be any considerable depth between the 
cover and the slide, as the mixture of acid and balsam assumes a 
rather deep colour. A slight modification of this plan may be 
used with advantage to prevent delay in the drying of the slide, as 
follows : Place the object (saturated with carbolic acid) in the 
middle of the slide, and make a little embankment of balsam at 
some distance all round it, then fill the space within the balsam 
with a pool of the acid, and place the slide under a cover till the 
acid and the balsam are sufficiently mixed (ten minutes or a 
quarter of an hour), then drop fresh balsam on the object and 
cover as usual. Turpentine is not suitable for this purpose, as it 
runs all over the slide. 
(3.) Mounting Moist Objects in Balsam .—In a note read before 
