132 



PRACTICAL TREATISE ON THE MICROSCOPE. 



which a new cover can be adapted with little trouble; the 

 tubular top is provided with a screw, upon the edge of which 

 the cover of thin glass or mica is laid, over this a cap is screwed 

 to keep the cover firm. Fig. 84 represents the tubular 

 top, with its screw cap, and fig. 85 a section of the entire 



Fig. 85. 



Fig. 84. 



instrument, A B being the flat support, c the object-plate or 

 tablet, d the channel around the same, b the tubular top with 

 its screw-cap, e, holding down the thin glass cover, a. When 

 the glass cover is of tolerably stout glass, these cages, besides 

 being only employed for animalcules, may be used for com- 

 pressing such objects as are soft, but still too opaque to be 

 seen through. When these are moderately compressed, their 

 structure is readily made out ; but an instrument constructed 

 for this purpose especially, and known as the Compressorium, 

 will be presently described. 



To use these animalcule cages, all that is necessary is to 

 place a small quantity of the fluid containing the animalcules 

 upon the object-plate or tablet, and to slide the cover carefully 

 until the drop is flattened out to the required degree of thin- 

 ness; this should never exceed the size of the tablet itself. 

 When the drop of fluid is made flat, the objects it contains 

 may not only be viewed with great ease and convenience, but 

 they may be carried about and kept for some considerable 

 time under observation ; the capillary attraction will preserve 

 the fluid between the two glasses, and no shaking or turning 

 that is not sudden will injure them in the least. When more 

 fluid than is necessary is placed upon the bottom glass, the 

 excess will escape into the channel, and, in all probability. 



