414 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
depends on the different composition, as shown in the following 
analyses : — 
English Cover-glass. 
Other Cover- glass. 
SiO„ 
71-00 
74-77 
Al., 0 3 
0-57 
0-45 
CaO 
13-76 
10-75 
MgO 
0-31 
0-33 
K„0 
0-20 
0-20 
Na 2 0 
14-16 
13-50 
100-00 
100-00 
In the first case the proportion of lime to alkalies is greater than in 
the second, and to this is clue one of the most important properties of 
the English glass, viz. its resistance to the effect of moisture and other 
agents. 
For delicate, easily perishable microscopic preparations, then, a highly 
resisting glass with very high content of lime is absolutely essential, 
although the production of cover-glasses is thereby rendered very 
difficult. 
The usefulness of a glass for delicate preparations may be tested by 
observation of its behaviour on keeping for a long time in air free from 
dust, or more expeditiously by the effect upon it of dilute hydrochloric 
acid during 24 hours. 
Method of Mounting Calcified Microscopic Specimens.* — Mr. J. 
Mansbridge gives the following description of the method of mounting 
which ha has adopted for certain dry calcified sections where it is 
advisable to retain air in the structure for purposes of clear definition. 
“ One great disadvantage in the use of a fluid balsam as a mounting 
medium for this class of sections, is the liability to run into any spaces, 
such as lacunae or tubuli that may exist in the tissue, and thus render 
the specimen useless. To overcome this difficulty I have used with 
success desiccated balsam in the following way : — Take a clean slide, 
place it upon a hot table with a small single lump of balsam upon it ; 
use sufficient heat to slowly melt the balsam, which must not be made 
too hot. When sufficiently fluid lay the section upon it and cover with 
a hot cover-glass, which must be pressed down in such a way as to expel 
all air from beneath it. Remove the slide to a cool surface and continue 
to keep pressure upon the cover-glass for a few minutes, when the 
balsam will be found to be quite hard and the specimen ready to be 
labelled and put away finished. 
The advantages of this method are, I think, (1) There is no chance 
of the mounting medium running in and spoiling the sections, as it 
becomes perfectly hard a few minutes after removal from the hot table. 
(2) The specimen is finished at the time and is ready for the cabinet. 
There is no need to use a clip, and no fear of the cover-glass shifting if 
the slide is placed upon its side. (3) It is very convenient for teaching 
purposes, as the ordinary stiff balsam in a bottle furnished with a glass 
* Trans. Odont. Soc. Great Britain, xxv. (1893) p. 176. 
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