THE MICROSCOPE. 31 



secured for examining it. The petals of plants, 

 the wings and other parts of insects, with many 

 other objects, can only be examined in this way. 



Fig. 15. Stage Forceps. 



Even the beginner will find it useful to keep by 

 him some little bottles, containiog certain chemical 

 re-agents. Thus, a solution of iodine is useful to 

 apply to the tissues of plants, for the purpose of 

 ascertaining the presence of starch. This solution 

 may be made by adding five grains of iodine and 

 five grains of iodide of potassium to an ounce of 

 distilled water. It turns starch blue and cellulose 

 brown. Cellulose is the substance that forms the 

 walls of the cells in plants. Dilute sulphuric acid 

 (1 to 3) is also useful as a re-agent ; if applied to 

 cellulose previously stained with iodine, it imparts 

 a blue or violet tint. Strong nitric acid turns 

 albuminous matter a deep yellow; and when 

 diluted (1 to 4) with water is used for separating 

 the elementary tissues of vegetable substances either 

 by boiling or maceration. 



The strong solution of potash (liquor potassae) 

 can also be employed with advantage in softening 

 and making clear opaque animal and vegetable 

 substances. While using these powerful agents, 

 great care should be taken to prevent the trans- 

 parency of the object-glass becoming impaired by 

 contact with them or by long exposure to their 

 vapours. 



