350 MANIPULATION. 



give firm support to a loaded cork. Various descriptions of 

 earthenware troughs are kept on sale in shops, that will answer 

 very well for many purposes; these are certain kinds of 

 square soap dishes, some provided with covers, others not. 

 Saucers of various sizes, small covered jars in which potted 

 meats, pomatum, and substances of a like kind are kept, will 

 be found very useful occasionally. Convenient troughs may 

 also be made of pieces of stout plate-glass, cemented together 

 by marine-glue ; their edges should be ground flat, so that 

 another piece of plate-glass may be laid on to form a cover. 

 Those troughs that are white in the inside may be made 

 black with seaHng-wax varnish, but in these spirit cannot be 

 employed. The most convenient sizes for troughs in which 

 injections are to be examined under the compound microscope, 

 are three inches square and one inch deep, or three inches 

 long, two inches wide, and one inch deep ; much larger sizes 

 than these cannot well be supported on the stage-plate. 

 When small objects are necessary to be dissected by trans- 

 mitted light, some of the cells described at page 294, may be 

 employed, the plate-glass allowing the light to pass through 

 readily. Mr. Pritchard supplies with his microscopes some 

 little brass troughs, with glass bottoms ; these can be fixed to 

 the stage-plate by a bayonet catch, and will be found exceed- 

 ingly useful. 



Loaded Corks. — These consist of flat pieces of cork, of 

 various degrees of thickness, that are covered over on their 

 under surfaces with sheet-lead of sufiicient weight to make 

 them sink in fluid. The lead may either be cemented to the 

 cork, or it may be cut a little larger than it, and folded over 

 the edges rather loosely, so that when the cork is expanded 

 by the fluid, it may not rise up in the middle. If a loaded 

 cork is not at hand, its place may be supplied by a plate of 

 the required size, kept steady by flat weights of lead. Some 

 persons employ plates of wax, or a little of the same substance 

 melted into the bottom of the trough, as a substitute for the 

 loaded cork, but the pins do not hold in it very well. Mr. 

 Goadby has described a plan* of securing insects about to be 

 * Transactions of the Society of Arts, vol. 1., part ii., page 111. 



