MICROSCOPIC OBJECTS. 157 



or varnish for the gum or isinglass would readily 

 suggest itself to any practical chemist engaged in 

 these matters. 



(5.) On Preserving Objects in Fluids. — Take a slip of 

 glass and spread a little white lead ground in oil on the 

 upper side, leaving an aperture in the middle to receive 

 the object. This paint being laid on of the thickness 

 of the object, the little pool or cavity is filled with weak 

 spirits of wine ; then lay in your object. Having pro- 

 cured a piece of thin glass of the proper size, lay it on 

 the top, and with a stick of wood rub it close down on 

 the paint, beginning at one end and passing across the 

 slider to the other, so as to exclude all air bubbles. In 

 this way the dehcate vessels of plants, &c. may be pre- 

 served. I have mounted animalcules and small Crustacea 

 in this way with complete effect. Active molecules may 

 be kept thus mounted for months. Other fluids, such as 

 solution of common salt or corrosive sublimate, might 

 in some cases be preferable to spirits. 



(6.) When the objects are large and do not require a 

 very high power, they may be cemented on the slip of 

 glass itself with a piece of black paper under them, or a 

 wafer may be fastened to the under side of the glass, 

 to give a back ground when viewed as opaque objects, 

 and removed when examined by trans.mitted light ; 

 or a black cylinder of cork may be held under a trans- 

 parent object to view it by reflected light. The 

 mode of mounting large objects on slips of glass with 

 paper under them is here shown. These sliders should 



