THE POLYSOOPIC CELL. 81 



the following reasons: After mounting the specimen, the only thing necessary 

 when it is desired to study it under the microscope is to place a drop of immersion 

 oil on the top of the cell and press over it a tiny piece of cover glass. This 

 causes a perfect transparence of the top of the cell and makes the inclosed specimen 

 visible. The only special advantage of having the cell polished is to enable one to 

 determine quickly the position of the specimen within. An advantage of leaving 

 the cell with ground sides is that the number and name of the specimen may be 

 written easily upon the surface with India ink. 



METHOD OF USE. 



The slide once made (Plate I, fig. 8), the method of preparing and 

 mounting the specimen is a very simple one. Having passed it through 

 all the fluids to the xylene, the portion of the insect which it is desired 

 to preserve is dissected away and placed in the tube of the cell which has 

 previously been filled with Canada balsam dissolved in xylene. The 

 specimen, which should be just large enough to slip into the tube readily, 

 is pushed in by means of a pin or other suitable instrument and the ends 

 of the tube sealed with slide cement of the kind generally used by tlie 

 worker. 



Sometimes it may occur that the specimen is slightly smaller than 

 the caliber of the tube and, in order to hold it in a fixed position therein, 

 recourse may be had to a bent bristle which is pushed in until it comes 

 in contact with the specimen. (Plate I, fig. 9.) A tiny piece of filter 

 paper or other convenient substance will serve the same purpose, as shown 

 in the figure indicated. 



Cells of the kind described here may be stored as easily as ordinary 

 microscopical slides by either placing them in a drawer with compart- 

 ments numbered to correspond with their numbers or else in small en- 

 velopes. Where slide cabinets with compartments of sufficient depth are 

 available, an excellent plan is to fasten each cell to an ordinary slide by 

 means of a minute drop of balsam which, while retaining it in place for 

 storage, may be dissolved easily when it is necessary to work with the 

 specimen. 



CELL HOLDER. 



Wien using the preparation for study, the cell may he held in place 

 upon a special holder which I have devised for this purpose. It consists 

 of an aluminium plate 35 by 75 millimeters, having an opening 10 by 30 

 millimeters, in which a small glass slide may rest upon a flange and upon 

 which the cell may be placed and clamped as shown on Plate II, figs. 

 1 and 2. This piece of apparatus is not necessary if one has slide clips 

 on his microscope long enough to rest upon the ends of the cell, and thus 

 retain it in position for work with the camera lucida or in making 

 photomicrographs. 



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