EXAMINATION OF LIVING BACTERIA. 15 
(2) Manipulate condenser, diaphragm, and mir- 
ror to determine the best adjustment for the exam- 
ination of unstained bacteria. 
2. Examination in the ‘“‘Hanging Drop.” 
Fic. 3.—A ‘concave slide’ with ‘hanging drop” 
(McFarland). 
Fic. 4.—A slide with cell for hanging drop. The ring 
may be made of glass or of zylonite, and is cemented on 
the slide with Canada balsam. 
(a) Paint a ring of vaselin around the hollow in 
water, and keep in alcohol; or wash in strong nitric acid 
for some time, rinse in water, and store in alcohol. Very 
often simply passing them several times through a Bunsen 
flame will clean them sufficiently. 
