350 GUIDE TO CALIFORNIA INSECTS. 



1. See that the slide containing the object is clean, and free from dust and 

 then lay it on the stage of the microscope. 



2. Look down the tube and manipulate the mirror till securing the strongest 

 light. If the field is cloudy revolve the eyepiece so as to locate the dirt. 



3. Move the object as nearly as possible to position and lower the tube of the 

 microscope till the objective is as close or closer than the focus, doing this 

 with the eye almost on the level of the stage. 



4. Bring the eye to the tube again and turn the focusing screw up (never 

 down) till the object comes into view. 



If the instrument needs cleaning bring the fact to the attention of the in- 

 structor rather than to try to clean it yourself; however the method of cleaning 

 follows: (a.) brush off all dust. (b.) moisten lens with the breath and 

 wipe gently with a clean cloth. (c.) if these means fail slightly moisten a 

 a cloth with a drop of alcohol and apply carefully. 



MICROSCOPICAL MOUNTS. 



Microscopical slides are usually made with an aqueous medium or with 

 balsam. Aqueous media are water, sugar solution, mucilage or glycerine 

 jelly. To make these mounts permanent they must be sealed. One of the 

 best method of sealing an aqueous mount is to first mount the preparation 

 between two coverglasses, one much smaller than the other. Now place a 

 drop of balsam on a slide and lay the mount small cover down in the balsam. 



Balsam mounts require the removal of the water from the specimen which 

 is usually accomplished by the use of alcohol. The alcohol is then replaced 

 by an oil which in turn is largely replaced by the balsam. The oils most used 

 are xylol, turpentine, clove oil and cedar oil. Carbolic acid is sometimes 

 added to the turpentine. When the object is dry it can be placed at once in 

 the oil or even directly into the balsam. 



SECTIONING INSECTS. 



For the most careful study of the structure of insects sections are cut bu the 

 use of a microtome. The following method gives good results: 



1. Place the specimens in a two dram hoho vial, not filling it more than a 

 tenth full, and kill by filling with boiling water. 



2. Harden tissues with alcohol pouring off % the water and adding alcohol. 

 In half an hour pour off a third and add as much alcohol. An hour later Va and 

 the next day put in fresh strong alcohol. 



3. Remove the alcohol by soaking a few minutes in oil of cloves and then 

 place in melted parafine (56 degree.) one or two days, when it is ready to cut 



