6 ELEMENTARY BACTERIOLOGY LABORATORY EXERCISES 
EXERCISE 4 
MICROSCOPIC MEASUREMENTS 
By use of a stage micrometer, determine the value of the divisions on your 
ocular micrometer. Having calibrated the ocular micrometer, make measure- 
ments of a number of representative bacteria found on your stained slides. More 
delicate measurements may be obtained with the aid of a filar micrometer 
ocular. 
EXERCISE 5 
EXAMINATION OF LIVING BACTERIA 
Hanging Drop Preparation 
Clean a cover glass and place it in a pair of forceps. Clean a hanging drop 
slide and spread vaseline around the edge of the depression. Place a small drop 
of the infusion in the center of the cover glass. Quickly invert the forceps and 
cover glass so that the drop hangs. Carefully place the cover slip with the 
hanging drop over the depression. Press down the cover slip on the slide in 
order to seal and thus prevent evaporation. See that the drop hangs from the 
cover glass without touching the side or bottom of the cavity. 
Exclude most of the light by means of the iris diaphragm and examine first 
under the 16 m.m. objective to locate the edge of the drop. Having found this, 
raise the tube and swing the 4 m.m objective into place. While watching the 
objective from the side, run it down until the tip of the objective almost comes 
in contact with the cover slip; then slowly and carefully focus upwards, regulat- 
ing the light in the meantime by means of the iris diaphragm, until the bacteria 
come into view. 
Study carefully. Note especially the difference between true motility and 
Brownian movement. Make drawings. 
Cover Glass Preparation 
While not so satisfactory as the hanging drop method, living bacteria may 
be observed by simply placing a drop of the culture on an ordinary slide and 
covering it with the cover glass. 
EXERCISE 6 
MORPHOLOGY OF MOLDS, YEASTS, AND PROTOZOA 
Make a wet preparation of the culture of yeast furnished. Make drawings. 
Examine the mold cultures, furnished on agar plates, under the 16 m.m 
