340 



ACCESSOKY APPARATUS 



socket. 1 The supporting plate being perforated by a large aperture, 

 the object may be illuminated by the Lieberkiihn if desired. The discs 

 are inserted into the holder, or are removed from it, by a pair of 

 forceps constructed for the purpose ; and they may be safely put 

 away by inserting .their stems into a plate perforated with holes. 

 Several such plates, with intervening guards to prevent them from 

 coming into too close apposition, may be packed into a small box. 

 To the value of this little piece of apparatus the Author can bear 

 the strongest testimony from his own experience, having found his 

 study of the Foraminifera greatly facilitated by it. 



Glass Stage-plate. Every microscope should be furnished with 

 a piece of plate glass, about 3^ in. by 2 in., to one margin of which a 

 narrow strip of glass is cemented, so as to form a ledge. This is 

 extremely useful, both for laying objects upon (the ledge preventing 

 them together with their covers, if used from sliding down when 

 the microscope is inclined), and for preserving the stage from injury 

 by the spilling of sea-water or other saline or corrosive liquids when 

 such are in use. Such a plate not only serves for the examination 

 of transparent, but also of opaque objects ; for if the condensing 

 lens is so adjusted as to throw a side light upon an object laid upon 

 it, either the diaphragm plate or a slip of black paper will afford a 

 dark background ; whilst objects mounted on the small black discs 

 .suitable to the Lieberkiihn may conveniently rest on it, instead of 

 being held in the stage-forceps. 



Growing Slides and Stages. A number of contrivances have been 

 devised of late years for the purpose of watching the life histories of 



FIG. 290. 



minute aquatic organisms, and of ' cultivating ' such as develop and 

 multiply themselves in particular fluids. One of the simplest and 

 most effective, that of Mr. Botterill, represented in fig. 290, consists 

 of a slip of ebonite, three inches by one, with a central aperture of 

 three-fourths of an inch at its under side ; this aperture is reduced 

 by a projecting shoulder, whereon is cemented a disc of thin glass, 

 which thus forms the bottom of a cell hollowed in the thickness of 

 the ebonite slide. On each side of this central cell a small lateral cell 

 communicating with it, and about a fourth of an inch in diameter, is 

 drilled out to the same depth ; this serves for the reception of a supply 



1 A small pair of forceps adapted to take up minute objects may be fitted into 

 the cylindrical holder in place of a disc. 



