ANIMALCULE CAGE. 



71 



bottle, having a rim which will prevent its' falling through, is now 

 inserted in the loop thus formed, and is held tightly there by the ends 

 of the whalebone being drawn further through the ring, and thus 

 diminishing the size of the loop. The bottle thus fixed may be used 

 for dipping out the animalcules. Whalebone can be moulded to any 

 form by placing it for a short time near the fire. 



Animalcule Cage. Mr. Yarley, in the year 1831, greatly improved 

 the form of this instrument, and gave to it the name of capillary-tablet, 

 or cage. He made a channel all round the object-plate, so that the 

 fluid and the animalcules in it were retained at the top of the object- 

 plate by capillary attraction ; and they then bear turning about in all 

 directions without leaving the top, provided the cage be not suddenly 

 shaken. The cover is made to slide down upon the object-plate. The 

 plate of brass to which the tube supporting the tablet and cover is 

 attached is of a circular form, slightly flattened on two opposite sides 

 for convenience of package. One of these instruments is seen in ele- 

 vation and in section in fig. 52. A B, in both figures, is the flat plate 

 of brass to which the short tube carrying the object-plate or tablet is 

 fixed d the piece of brass into which the tablet c is fastened \ b the 

 tubular part of the cover, into the rim of which the thin plate of glass 

 a is cemented. 



r i 



fig. 52. 



fig. 53. 



Many microscopists make great use of the compressorium, an in- 

 strument in which an object may be submitted to graduated pressure 

 between two plates of glass, the parallelism of which is perfectly main- 

 tained. The class of investigations in which the eompressorium is 

 valuable, is that in which such structures as the minute ovum need be 

 closely scrutinised, without any further change in their shape than 

 may render their contents more distinctly visible. For such purposes 



