PKEPARATION OF A HANGING DROP 77 



slide and cover-glass must be placed in 1/1000 mercuric 

 chloride or some equally efficient disinfectant for at least 

 one hour before cleaning or reusing. 



4. Examine first with objective No. 3, then with object- 

 ive No. 7 or the 1/12 oil immersion lens, using ocular No. 1 

 in each case. After a perfect focus is obtained, ocular 

 No. 4 may be used if desired. 



Manipulation of Microscope. Using the lowest power 

 objective and ocular, focus the tube of the microscope 

 down by means of the coarse adjustment until the objective 

 nearly touches the cover-glass, being careful not to touch it. 

 Then, with the eye at the ocular, focus up with the coarse 

 adjustment and move the preparation until the edge of the 

 drop comes plainly into view. This focal point may be passed 

 without noticing it if the light is too intense or too dim. The 

 edge of the drop is a curved line. The preparation 

 should be so moved that this line cuts the center of the 

 field. 



Focus up slightly, swing the No. 7 or 1/12 objective as 

 desired, into place and after the field desired is obtained 

 with the coarse adjustment, focus down until the objective 

 nearly touches the cover-glass. Then with the eye at the 

 ocular, focus up carefully with the coarse adjustment until 

 the edge of the drop comes plainly into view. Use the fine 

 adjustment to bring out details. 



In using the 1/12 oil immersion lens a small drop of im- 

 mersion oil is placed in the center of the cover-glass, the 

 1/12 objective swung into place as above. Greater care 

 must be exercised in focusing, as this objective has a shorter 

 working distance. 



