1896 THE MICROSCOPE. 45 



small quantities, when used, and the stock bottles kept tightly 

 corked. 



238 Since the concave mirror gives far better results than the 

 plane one, what is its use f Wistaria. 



When properly focussed upon the object the concave mirror 

 acts as a simple condenser, and is more useful with the higher 

 objective whose smaller lenses require a brighter light for good 

 definition, the plane mirror is generally used when a bull's-eye 

 lens or other condenser of light is employed, the plane surface 

 being used to direct the light into the objective. If, in tliis case, 

 the concave mirror were employed it would increase the aber- 

 ration of the condenser as well as those of the objective, and 

 poor definition would result. 



PRACTICAL SUGGESTIONS. 



By h. A. WILLSON, 



CLEVELAND, OniO. 



A Home-Made Turn-Table . — The following is primitive 

 and was used before the advent of turn-tables, but for one who 

 is not prepared to purchase a store turn-table it will answer 

 fairly well. 



A flat piece of board of the proper size will answer for the 

 table. On this table place two circular wheels secured in place 

 by central screws. On one disk place spring clips of brass to hold 

 a slide ; on the other wheel fix a handle. Connect the wheels 

 by an endless band. To hold the band the wheel should be 

 grooved. 



Tongues of MoHusca, — These tongues, or palates may be ob- 

 tained by expert dissection. An easier method, however, is to 

 boil the animal in caustic potash until all the soft parts have 

 disappeared. The tongue, or palate will then be found at the 

 bottom of the vessel and may then be separated with dissecting 

 needles. When properly prepared they are beautiful objects 

 for the polariscope. 



The Itch Insect — Acarus Scabiei. — This insect is very in- 

 teresting and a rare object in a microscopical cabinet. To find 



