MOUNTING AND PRESERVING OBJECTS. 81 



a useful instrument for making moderate pressure on the 

 glass cover until the cement on its edge is dry. A drop- 

 ping-tube with a bulbous funnel, covered with thin india- 

 rubber, for taking up and dropping small quantities of 

 fluid, w r ill also be of service. 



Superfluous fluid may be removed from the edge of the 

 cover by a piece of blotting-paper, care being used not to 

 draw away the fluid beneath the cover. 



As soon as objects are mounted, the slides should be 

 labelled before cementing is finished, otherwise time will 

 be lost in searching for a particular object among others, 

 or the name may be forgotten. 



Boxes of wood or of pasteboard, with grooved racks at 

 the sides, are occasionally used for preserving a collection 

 of specimens. It is better, however, to have a cabinet 

 with drawers or trays so that the specimens may lie flat, 

 with their ends towards the front of the drawer. A piece 

 of porcelain on the end of the drawer is convenient for 

 the name of the class of objects contained, to be written 

 on with lead-pencil. 



Collecting Objects. The methods pursued by naturalists 

 generally will suffice for a large proportion of the objects 

 which are matters of microscopic inquiry, but "there are 

 others which, from their minuteness, require special search. 

 Many fresh-water species of microscopic organisms inhabit 

 pools, ditches, and streams. Some attach themselves to 

 the stems and leaves of aquatic plants, or to floating and 

 decaying sticks, etc. Others live in the muddy sediment 

 at the bottom of the water. A pond stick has been con- 

 trived for the collection of such organisms, consisting of 

 two lengths, sliding one within the other, so that it may 

 be used as a walking-cane. In a screw socket at one end 

 may be placed a curved knife for cutting portions of plants 

 which contain microscopic parasites; or a screw collar for 

 carrying a screw-topped bottle, which serves to bring up 

 a sample of liquid ; or it may have a ring for a muslin net. 



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