150 PREPARATION OF OBJECTS FOR THE MICROSCOPE. 



they would be exactly what is wanted for fluid mounting; for 

 the great requisite in fluid mounting is a cell that is a little soft 

 or yielding, so that the thin glass cover will come down into close 

 contact with the cell all around. When this is the case, you can 

 quickly take up the fluid that runs out, with a camel's hair brush, 

 and at once apply a coating of cement to the edges of the thin 

 glass, and your slide requires no further care. But if the thin 

 glass cover does not fit closely to a cell, the air will be very apt 

 to get in while you are drying it ; and when you come to put on 

 the cement, that will be almost sure to run in. 



The marine glue, with which I thought to cover the wax cells, 

 is a composition of equal parts of India rubber and shellac, dis- 

 solved in mineral naphtha. It has long been considered the most 

 adhesive and permanent cement that can be made ; and from the 

 large quantity of rubber in it, it would seem as if it ought to be 

 impervious to all the liquids used in mounting. 



In applying these wax circles to the slide, a little care is neces- 

 sary, that no air bubbles remain between the wax and the glass, 

 nor in the cement which covers the cell. First, make a ring of 

 cement on the slide, with a small camel's hair brush, of the same 

 size of the wax ring. Then lay on the ring, accurately centering 

 it on the turn table, and press it down under a piece of writing 

 paper held on it in such a way that the ring underneath cannot 

 be displaced. It is well to let this dry for a day. Then cover 

 the top and the edges of the cell with one or two coats of liquid 

 marine glue, and in two or three days it can be trimmed with the 

 point of a knife blade, cleaned and used for mounting. 



As a preservative fluid, one can use carbolated water four or 

 five drops of carbolic acid to each ounce of filtered water or 

 camphorated water that in which a little fine camphor has been 

 mixed and afterwards filtered or any other preparation of water 

 which will prevent fungoid growths, or in other words preserves 

 the objects. Put enough of the liquid in the cell to fill it full, 

 immerse and arrange the objects in it, and then let a thin glass 

 cover of the proper size come gently down on the liquid. It 

 will infallibly press out all the air and settle gradually on the 

 cell ring, pushing out all superfluous fluid. A gentle pressure 



