THE MICROSCOPE 13 



7. In looking through the microscope keep both eyes open. 

 A little practice will enable you to neglect wholly the -image in 

 the unused eye and will avoid the muscular strain due to the clos- 

 ing of one eye. It is well to use right and left eyes alternately. 



8. Keep the stage of the microscope horizontal. It is 

 always better to adjust the height of your chair than to tilt the 

 microscope. 



9. Do not use the stage clips unless it is absolutely neces- 

 sary. Turn them back so that they will not be in the way. 



II. Exercise in the Use of the Microscope 



1. Inversion of the image in the microscope. Place 

 the card which has been given you upon the stage of the mi- 

 croscope in proper position for reading. Find a letter "e" 

 and without shifting the position of the card draw, in outline, 

 40 mm. high. 



2. On the slide containing mounted colored fibers determine 

 the relative positions of the fibers by focusing up and down. Use 

 the high power objective. In this exercise amount of color must 

 not be confused with sharpness of focus. A dark color out of 

 focus may strike the eye more forcibly than another color which 

 is in the plane of focus. Distinctness of the margins or outlines 

 of the fibers is the only safe point for comparison. In your notes 

 indicate relative positions of the fibers beginning with the lower- 

 most (1, 2, 3, etc.). While your slide is still on the microscope 

 ask to have your observations verified. No drawings required, 



3. Examine dry cotton fibers with low and high powers of 

 miscroscope. Allow a drop of water to run under the coverglass 

 by applying a pipette to the slide at the edge of the coverglass. 



Make a drawing of the wet fiber 10 mm. in diameter, being 

 sure to include in your drawing at least one place where the 

 fiber is twisted. If you have studied the fiber carefully you 

 should be able to come to a definite conclusion regarding its form 

 as an object with three dimensions. At the side of the drawing 

 already made, place a diagram illustrating your conclusion re- 

 garding the shape of a cross-section of this fiber. 



