9 
6. While looking into the ocular, and while moving the slide slowly back 
and forth, turn the fine adjustment so that the tube moves upward. Turn 
slowly until the image appears sharp and clear. 
7. Draw and describe preparation A as seen with the oil immersion object¬ 
ive. It is not necessary to draw all of the organisms seen in a field. The 
drawings should be large enough to show the exact shape of the organisms in 
outline. 
8. Examine preparation B with the oil immersion objective. Draw a field 
from the prepapration. 
9. Examine preparation C with oil immersion objective. Draw a field 
from the preparation. 
10. According to shape, name the bacteria in preparations A. B. and C. 
(See Fig. 5.) 
11. Draw and describe the organisms in preparations D. showing spores 
and in E. showing flagella. 
12. Knowing the diameter of the field of the oil immersion objective, 
(see paragraph 14), estimate the size in millimeters of the organisms in pre¬ 
parations A and B. 
13. The micron (written y) is the standard of measurement for bacteria. 
1 micron—0.001 m. m. 
(a) Give the estimated size of the organisms in microns. Show 
the calculations in each case. 
14. The diameters of the real fields of the objectives most commonly used 
are given in the following table: 
DIAMETER OF REAL FIELDS OF OBJECTIVES 
Objectives. 
Diameter of Field 
Using lOx (1 inch) Eyepiece 
and a tube length of 160 m. m. 
16 m. m. (f in.) 
1.55 m. m. 
4 m. m. G in.) 
0.31 m. m. 
1.8 m. m. (^ in.) 
0.16 m. m. 
Note.—As soon as the work with the oil-immersion objective is completed, 
it should be wiped off with lens paper. 
