232 MOUNTING OBJECTS IN CELLS. 



by the Dropping-bottle or Syringe, and any minute air-bubbles 

 which may be seen adhering to its bottom or sides must be removed 

 by the needle ; the object, previously soaked in fluid resembling 

 that with which the cell is filled, is then to be placed in the cell, 

 and should be carefully examined for Air-bubbles on all sides, and 

 also by looking up from beneath. This examination should be 

 made with a Hand-Magnifier or Simple Microscope ; Quekett's 

 Dissecting Microscope (Fig. 29) being so especially suited to the 

 purpose, that the Author never mounts an object in fluid without 

 making use of it. "When every precaution has been taken to free 

 the cell from these troublesome intruders, the cover may be placed 

 on it, one side being first brought down upon its edge, and then the 

 other ; and if the cell have been previously brimming over with 

 fluid (as it ought to be), it is not likely that any air-space will re- 

 main. If, however, any bubbles should present themselves beneath 

 the cover, the slide should be inclined, so as to cause them to rise 

 towards the highest part of its circumference, and the cover 

 slipped away from that part, so as to admit of the introduction of a 

 little additional fluid by the pipette or syringe ; and when this has 

 taken the place of the air-bubbles, the cover may be slipped back 

 into its place.* All superfluous fluid is then to be taken up with 

 blotting-paper ; and particular care should be taken thoroughly 

 to dry the surface of the cell and the edge of the cover, since 

 the varnish will not hold to them if they be in the least damp 

 with water. Care must also be taken, however, that the fluid be 

 not drawn away from between the cover and the edge of the cell 

 on which it rests ; since any deficiency here is sure to be filled up 

 by varnish, the running-in of which is particularly objectionable. 

 These minutiae having been attended to, the closure of the cell 

 may be at once effected by carrying a thin layer of Gold-size or 

 Asphalte around and upon the edge of the glass-cover, taking care 

 that it touches every point of it, and fills the angular channel 

 which is left around its margin. If the wall of the cell be very 

 thin, it will be very advantageous to include it in the ring of 

 varnish, so as to make it hold down the cover, not only on the cell, 

 but on the slide beneath ; and this will help to secure it against 

 the separation of the ring from the slide, which is apt to be 

 produced by a 'jar' after the lapse of time. The Author has found 

 it advantageous, however, to delay closing the cell for some little 



* Mr. Quekett and some other practised Manipulators recommend 

 that the edges of the cell and that of the disk of glass be smeared with 

 the gold-size or other varnish employed, before the cell is filled with 

 Quid; but the Author has found this practice objectionable, for two 

 reasons, — first, because it prevents the cover from being slipped to one 

 side (which is often desirable) without its being soiled by the varnish, 

 — and second, because when the edge of the cell has been thus made to 

 ' take ' the varnish, that which is afterwards applied for the closure of 

 the cell is more likely to run in, than if the whole of the surface covered 

 by the glass is moistened with an aqueous fluid. 



