14 ZOOLOGY DIEECTIONS 



4. Place wool fibers on a clean slide. Apply coverglass and 

 study when dry and when wet as for cotton. Examine the out- 

 line of the fiber carefully. Draw a wet fiber, 10 mm, in diame- 

 ter, and a cross-section as directed before. 



What diiferences do you observe between the dry and the 

 wet fibers? Notes required. 



5. Mount a drop of protozoan culture in such a way as 

 to include minute air bubbles. The inclusion of cotton fibers with 

 the drop of water will facilitate the formation of the air bubbles. 

 Study air bubbles and Protozoa and other micro-org'anisms with 

 special reference to the use of the focusing and lig-hting adjust- 

 ments of the microscope. No drawings are required, 



6. To determine the size of microscopic objects. One of 

 the commonest means of measuring microscopic objects is by 

 means of an ocular micrometer. The oculars for which these 







'^^^^ 



Figure B. The use of an ocular mierometer. A cell under the low power 

 of the microscope. Note that the cell is 14 of the smallest micrometer 

 divisions in length. Its acutal length is then : 14x0.0078mm.=0.10& 

 mm. Since the scale in the ocular remains the same regardless .of 

 the objective used this cell under high power would be about 64 of 

 the smallest micrometer divisions in length. Consequently each divi- 

 sion would have a correspondingly smaller value. 



directions are given have a scale divided by fine lines into 100 

 units of length. The lines appear in the field of the microscope 

 at the same time that the image to be measured is seen. Notice 

 that the upper portion of an ocular micrometer may be pulled 

 out or shoved in to permit of sharp focusing upon the ruled scale. 



