OF MICROSCOPIC OBJECTS. 31 



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 icory cell. This is a 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 not expensive. 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 nre 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 



