COMMON OBJECTS WORTH EXAMINING. 299 



7. Insects, if small, are to be examined alive and 

 as opaque objects. They may be imprisoned in a deep 

 cell with a thin square cover above them. If the cover 

 tends to slide off when the microscope is inclined, al- 

 low a very small drop of water to run under one cor- 

 ner, and the capillary attraction will then hold it in 

 place, but the quantity of water must not be sufficient 

 to extend into the cell. If the insect is small it may 

 be killed by an immersion in a strong solution of car- 

 bolic acid, and then transferred to Canada balsam, as 

 described in the books devoted to microscopical 

 mounting. This treatment often renders the body 

 beautifully transparent,, forcing out the proboscis and 

 spreading the legs in a very satisfactory manner. 



8: Gizzards. — Pull off the head of a common cricket 

 or katydid, and the gizzard will usually be obtained as 

 an oblong, hard, reddish-brown enlargement attached 

 between the oesophagus and the upper part of the ali- 

 mentary tube below the larger food-sacks. Free it 

 from these, cut it open lengthwise, and wash the in- 

 terior with a camel's hair brush. View it as a trans- 

 parent object. The grinding-teeth are well worth 

 studying. The gizzards of some beetles are also in- 

 teresting. They, however, are to be dissected out 

 with fine scissors and needles, work that is best done 

 under water. 



9. Scales of Fish are obtainable in great variety, 

 and make beautiful objects for low powers. They are 

 often coated with a tenacious mucous material which 

 may be removed by washing in a solution of caustic 

 potassa. They should be examined in water or in 

 glycerine. 



10. Hair. — The hair of animals, from the human 



