ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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affected by changes of temperature and of having a high refractive 
index. An advantage of special importance is that it remains perfectly 
colourless for any length of time, while balsam, in a few years at most, 
becomes yellow, and finally so opaque that the preparation is worthless. 
The soft, natural appearance which objects mounted in glycerin have 
renders any extra labour incurred in their preparation a matter of little 
moment to the artistic manipulator. 
The difficulty experienced in the manipulation of glycerin deters 
many from its more frequent employment. If attention is paid to 
details, however, it will be found but little more difficult to use than 
balsamic mediums. In order to bring out the points of importance, a 
brief description of the preparation of an ideal mount will be expedient. 
Attention is first directed to the material and apparatus used. 
The glycerin should be pure, and free from dust and air-bubbles. To 
keep it free from these contaminations, devices such as are recommended by 
Carpenter and Prof. James are excellent. These are bottles containing 
the glycerin, and provided with glass tubes, whereby the glycerin is 
forced out by air-pressure. 
The cements may be of a balsamic nature, but preferably zinc oxide 
or asphalt. Any cement not affected by the medium may be employed, 
but experience has proven that the two above named are the best. 
The other essential parts of the completed mount are the slip and 
cover-glass. No special mention is required concerning these except 
that they should be perfectly clean. To ensure this, the practice of 
leaving them until ready for use in a bath of ordinary battery fluid is 
recommended. 
In preparing a mount, the operations naturally divide themselves 
into four divisions, coming under the heads — (1) preparing the cell ; 
(2) preparing the section ; (3) placing section in the cell ; and (4) 
securing the cover-glass to the cell. 
Under the first head attention is called to three points, viz. thickness 
of the cement, depth of cell, and age of the cell. Upon the consistency 
of the cement depends in a great measure the formation of a good cell. 
It should not be thin enough to spread, yet should flow readily and 
smoothly from the brush. The depth of the cell should be such that a 
complete support shall be provided for the cover-glass without causing 
it to bear upon the object when cemented down, and yet should not be 
of such a depth as to interpose an unnecessary stratum of glycerin 
between the section and cover-glass. 
Of more importance, perhaps, than any other point, is the direction 
regarding the age of the cell. It is a common practice to ring a cell 
and use it while fresh, the manipulator arguing that a more perfect union 
of cell-wall and cover-glass is secured in this manner. Perhaps this is 
true, but it is at the expense of the slide’s usefulness. An author 
already quoted is authority for the statement that an ordinary balsam 
cell will, in drying, shrink 30 per cent. 
Under these conditions and in view of the fact that glycerin is non- 
compressible, something must give way when the cell contracts; and 
this is either the cover-glass or cell-wall. Whichever it is, the final 
result is the destruction of the mount and loss of all the work involved 
in its preparation. This leads us then to make the following statement : 
