GENERAL BIOLOGY 



Never focus down upon the object, since by this method there is 

 danger of crushing the lens into the object. Keep one hand on the 

 fine adjustment when looking at an object and vary the focus con- 

 stantly to bring all the fine details of structure into view. 



4. Do not use higher power objective without cover glass over 

 object examined. 



5. Always use the lower power before the higher one ; and 

 always use the lowest possible power sufficient for distinct vision. 



6. Do not touch lenses with fingers. If the field is blurred or 

 the object dim either the cover glass or the lenses are at fault. If 

 the cover glass is dirty remove it and clean it; if the fault is in 

 the eye-piece the particles of dirt revolve when the eye-piece is 

 rotated. If the field is still dim the objective is dirty and must be 

 removed and cleaned. In cleaning the lenses never use anything but 

 clean tissue paper supplied for that purpose. If necessary, the 

 lenses may be moistened by breathing upon them; if this is not 

 sufficient, consult the instructor. 



7. Keep both eyes open, using either the right or the left. The 

 strain of microscopic work on the eyes is usually due to the fatigue 

 of constantly closing one eye. If you cannot see the object with 

 both eyes open use an eye-shade provided for that purpose. 



8. Never leave the laboratory without first placing the micro- 

 scope in its case and locking it and all your apparatus in your 

 lo-cker. 



II. PREPARING OBJECTS. 



The preparation of objects for examination under the micro- 

 scope is termed mounting. Objects are usually mounted on pieces 

 of glass 3x1 in., known as slides. Observe the following direc- 

 tions : 



1. If the object to be studied is a mass of cells, separate it into 

 very small pieces by means of teasing needles; if it is a fluid use 

 only a very small drop. If too much fluid has been used it will run 

 out from under the cover glass and the excess must then be soaked 

 up with filter paper. Temporary preparations are usually mounted 

 in water, permanent ones in balsam. 



2. The lenses of the microscope, the upper side of the cover 

 glass and the lower surface of the slide must be perfectly clean 

 and dry. 



3. Having placed the object in a small drop of mounting fluid 



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