MOUNTING OF MICROSCOPIC OBJECTS. II 



drawing its outline with a pencil, and on removing the slide making 

 a mark exactly in the centre of this drawing. Of course, when the 

 slide is replaced, this mark will apparently be in its centre, and thus 

 the balsam and object can be accurately placed in proper position. 

 The principal objection to this method, is that the slide is apt to slip 

 out of place, and thus to render accurate centering almost impos- 

 sible. A most admirable contrivance for this purpose, however, is 

 the "porcelain mounting plate," named under the head of non-essen- 

 tials. This is made of a photographic porcelain plate, 3x5 inches, 

 ground flat upon one side, on which are cemented at right angles to 

 each other, two small strips of glass, the one three inches in length, 

 and the other one inch. A mark is then made upon the plate with 

 a pencil, exactly i^ inches from one strip, and y z an inch from the 

 other, so that when the ordinary glass slip is placed upon the plate, 

 with one end in contact with the two strips, this mark is 

 seen exactly in the centre. The slip is held firmly in 

 place, and the white surface of the plate serves ad- 

 mirably as a background upon which to arrange the 

 object. 



At last we seem to be really done with all our pre- 

 liminary work, and ready for mounting. But wait 

 another moment. Though as before stated, the oil 

 of cloves is perfectly miscible with the balsam, and 

 a specimen may be transferred directly from the one 

 to the other, it is a very slow drier, and an object so 

 mounted might be months in hardening sufficiently 

 to handle, even if the utmost precaution be taken to 

 drain off all the superfluous oil. Fortunately we have 

 %be containing* an excellent remedy for this trouble close at hand, 

 mounting material. pouring & ^^ quantity of benzole, into a watch 



glass, we place in it one of the specimens, say a wing, and imme- 

 diately cover it with the small bell glass to exclude dust, and pre- 

 vent the evaporation of the benzole, which is exceedingly volatile. 

 And now at last we are ready for the mounting. 



One of the cleaned slips having been placed upon the mount- 

 ing plate, and its surface dusted off with the brush, a drop of bal- 

 sam of exactly the proper dimensions, is to be placed in its centre, 

 indicated by the mark upon the plate. And here, practice alone 

 must be our guide, for the amount must be varied according to the 



