38 LABORATORY STUDIES IN ZOOUKIY 



until the objective is in line with the tube. Its exact position 

 is indicated by the "click" of a friction stop. The object can 

 then be seen dimly. To sharpen its outlines employ the fine 

 adjustment turning only slightly to the right or left. It is always 

 safest to focus up slightly before changing the objective, thus 

 avoiding the danger of the high objective coming in contact 

 with the object. Use great care in changing from low to high 

 power. 



Thoughtful practice in the use of the compound microscope 

 soon results in effectiveness on the operator's part. Always 

 observe the following rules in using a compound microscope : 



1. Do not touch the glass of the objectives and oculars with 

 the fingers or any object. If the surfaces become soiled ask the 

 instructor's aid in cleaning them with lens paper. 



2. It is dangerous to both lens and object to focus downward 

 with the eye on ocular. 



3. Never permit the objective to touch the cover glass. 



4. Do not use high powers when low ones will do. 



5. Always carry your instrument by the handle arm. Other- 

 wise the adjustments may be injured. 



6. Do not leave mirrors or lenses exposed to direct sunlight. 



7. In case of trouble consult your instructor. When the 

 microscope does not appear to behave properly, it is safe to assume 

 that the trouble resides in the operator rather than in the 

 instrument. 



