134 PREPARATION AND MOUNTING 



bubbles are formed by the operation. The cover may be 

 fixed by the aid of gold-size, Japan, or any of the usual 

 varnishes, care being taken, as before, that all the compound 

 is removed from the parts to which the varnish is intended 

 to adhere. 



The glycerine jelly of Mr. Lawrance, before mentioned, 

 requires almost a similar treatment. " The objects to be 

 mounted in this medium should be immersed for some time 

 in a mixture of equal parts of glycerine and dilute alcohol 

 (six of water to one of alcohol). The bottle of glycerine jelly 

 must be placed in a cup of hot water until liquefied, when it 

 must be used like Canada balsam, except that it requires 

 less heat. A ring of asphaltum varnish round the thin glass 

 cover completes the mounting." 



The Infusoria (see Chapter IV.) are sometimes preserved 

 in liquid ; but present many difficulties to the student. 

 Different kinds require different treatment, and consequently 

 it is well, when practicable, to mount similar objects in two 

 or more liquids. Some are best preserved in a strong 

 solution of chloride of calcium, others in Thwaites' liquid, 

 whilst a few keep their colour most perfectly when in 

 glycerine alone. There can be little doubt that light is the 

 bleaching agent in most cases. Many of them, however, 

 are so very transparent that they present but faint, objects 

 for ordinary observation. For this reason, however, they are 

 sometimes dyed in solution of magenta or other colour, as 

 elsewhere noticed. The Desmidiacese require somewhat 

 similar treatment, and may be mentioned here. The solution 

 of chloride of calcium has been strongly recommended ; but 

 no preservative liquid seems to be without some action upon 

 them. Both of the above classes of objects should be mounted 

 in shallow cells, so as to allow as high a microscopic power 

 as possible to be used with them. 



ENTOMOSTRACA. In every ditch or place where vegetable 

 matter exists, these little active, jerking pieces of life are 

 certain to be found. They are covered with a horny trans- 

 parent shell, and are various in form. Mr. Tatcm gives the 



