106 MICROSCOPIC OBJECTS. 



with the gum-dammar cement ; many show well when 

 mounted in a solution of balsam in chloroform. 



Desmidie<e fyc. For the mounting of these lower forms of 

 vegetable life, see Algae; they are best collected by taking 

 the green scum from the margins of ponds situated in open 

 and exposed districts, and placing this green matter in a 

 white saucer nearly full of water : shade, all but an inch or so, 

 from the surrounding daylight; and in the space of a few 

 hours, if fresh, the Desmids will be found massed at the place 

 that has been left exposed to the light ; with a pipette they 

 may then be separated from the surrounding substances, and 

 mounted in a shallow cell with one of the preservative fluids. 

 They are found in the greatest quantity in the later summer 

 and the autumn months. 



Diatoms are collected in nearly the same manner as Des- 

 mids, from which they may be distinguished by their light 

 brown colour; they are often found growing in tufts upon 

 the marine and the freshwater Algae. Their mode of prepara- 

 tion is rather difficult ; but, in a few words, the following will 

 be found the best process : Burn the deposit in a platinum 

 spoon until it assumes the appearance of a white ash, then 

 boil in nitric acid for a short time, when most of the siliceous 

 valves will be found quite clean : the large glass tubes used 

 by chemists for collecting hydrogen and other gases will be 

 found, on account of their length, of great assistance in sepa- 

 rating the species according to their specific gravities ; they 

 may then be mounted dry, in balsam, or in some fluids, but 

 not silicate of potassa. 



The name of the species of Diatom, if known, must be im- 

 mediately written on the slide. This rule holds good with all 

 specimens, as, if a note is not made at the time, it is liable to 

 be forgotten. 



Entozoa. Many of this class of animals exhibit their ana- 

 tomy best when mounted in glycerine ; they also mount well, 

 after preparation, in balsam. If surrounded by germinal mat- 

 ter, the use of the carmine or other dye to be used as a stain 

 will cause the parasite to appear better, the dye staining the 

 surrounding mass and leaving the animal untouched : an 



