OF MICROSCOPIC OBJECTS. Sr 
great experience, because they are of such a nature that 
dampness can penetrate them. This fault can be almost, if 
not totally, removed by immersing them in some strong 
varnish, such as the asphalt varnish hereinafter mentioned; 
but they must be left long enough when affixed to the glass 
slide to become perfectly dry, and this will require a much 
longer time than at first would be supposed. 
There has, however, been lately brought out what is 
termed the ivory cell, This isa ring of ivory-like substance, 
which may be easily and firmly fixed to the glass slide by 
any of the commonly used cements, and so forms a beautiful 
cell for any dry objects. They are made of different sizes, 
and are notexpensive. Flat rings of brass turned down to the 
sizes of the circular discs of covering glass and of varying 
thickness are very neat and useful for mounting opaque 
objects: they can also be obtained in tin and zinc. 
Some of our best microscopic men have stated that they 
have been frequently disappointed by an accumulation of 
encrusted matter upon the inner surface of thin glass used 
to cover the cell enclosing any dry object, and therefore use 
a shallow pillbox, made expressly for this purpose, which 
must be strongly cemented to the slide. For examination 
the lid must be removed, whilst it must be closed to protect 
the object from dust when laid aside. Another worker of 
experience recommends a cell in a mahogany slide, over 
which, by aid of a stud as on a pivot, a bone disk can be 
turned: this is termed, “ Piper’s Revolving Cover Slide,” 
and can be procured at the opticians’. 
Sometimes slides are used which are made by taking a 
thin slip of wood of the usual size (3 in. by 1 in.), in the 
centre of which is cut a circular hole large enough to 
receive the object. A piece of thin glass is fixed underneath 
the slide forming a cell for the object, which may then be 
covered and finished like an ordinary slide. This has the 
advantage of serving for transparent objects for which the 
before-mentioned wooden slides are unsuitable. A slight 
modification of this plan is often used where the thickness 
