302 HOW TO WORK 



slide may be gently warmed over the lamp, and the thin glass pressed 

 clown upon the preparation by slight taps with a needle point. The 

 specimen may now be examined with a quarter, and afterwards with 

 the twelfth of an inch object-glass. A good deal of granular matter 

 will possibly obscure the delicate points in the structure. The slide 

 is again gently warmed, and, with the aid of a needle, the thin glass 

 is made to slide over the surface of the specimen, without the posi- 

 tion of the latter being altered, and then removed and cleaned. 

 The specimen is then washed by the addition of drop after drop of 

 strong glycerine containing five drops of acetic acid to the ounce. 

 The slide can be slightly inclined while it is warmed gently over the 

 lamp, in such a manner that the drops of glycerine slowly pass over 

 the specimen and wash away the debris from its surface. 



I find it better to place delicate specimens upon a circle of thin 

 glass about f of an inch in diameter, instead of upon a glass slide. 

 The circle is then placed in a wooden slide in the centre of which a 

 hole has been drilled of the proper dimensions to receive it. A ring 

 of gummed paper is placed at the back of the slide and to this the 

 round glass is fixed when the specimen has been covered with the 

 smaller circle of thin glass, and this has been properly fixed in its 

 place by cement. 



Dropping Bottles. -The most convenient instrument for dropping 

 the glycerine on the specimen is a little bottle, of two ounces 

 capacity, with a syphon tube drawn to a point, and a straight tube, 

 with an expanded upper part, over which is tied a piece of stout 

 sheet vulcanised India-rubber. PI. LVI, fig. 342. Upon com- 

 pressing the air, by pressing down the India-rubber, the glycerine is 

 forced drop by drop through the syphon tube and allowed to fall 

 upon the specimen. These little bottles can be obtained of 

 Mr. Matthews, Mr. Highley, and Mr. Collins. 



When several drops of pure glycerine have been allowed to flow 

 over the specimen, the thin glass cover, after having been cleaned, 

 is re-applied and pressed upon the specimen very gradually, but 

 more firmly than before. Any excess of glycerine is easily removed 

 by placing small pieces of clean blotting paper at the side of the 

 thin glass. If the preparation looks pretty clear when examined 

 with the twelfth, the glass cover may be cemented down with Bell's 

 cement, p. 48, and the specimen left for many days in a quiet place. 

 It may then be re-examined, the process of washing with glycerine 

 repeated, and further pressure applied until it is rendered as thin as 

 is desired. When this point has been reached, more glycerine with 

 acetic acid is to be added, and a plate of mica or the thinnest glass 

 cover, p. 287, applied, when it may be examined with the twenty- 



