LIVING BODIES AND CELLS 19 



Every movement of the specimen is magnified as much as the speci- 

 men itself. So great gentleness is needed in moving it under the ob- 

 jective or else it will be moved out of view altogether. The microscope 

 appears to reverse the sides of the specimen, so in order to move the 

 image in any direction the specimen must be moved in the opposite 

 direction. Care should be taken not to press the lens upon the speci- 

 men. If the lens becomes dirty or moist it should be gently wiped 

 with a soft, clean handkerchief. A little alcohol rubbed on will aid in 

 removing the dirt. 



17. Preparation of specimens. Specimens are examined 

 upon glass plates, called slides. The regulation size is 

 three inches long and one inch broad. Specimens must 

 be very thin, so as to show only a single layer of cells or 

 fibers. A liquid specimen should be a small drop; a powder 

 should be only a tiny speck. A solid specimen is prepared 

 in either of two ways. Its cells and fibers may be picked 

 apart by means of two needles ; but this destroys the 

 natural arrangement of the parts. So the method of 

 slicing off extremely thin layers with a sharp razor is 

 more often used. This requires special training. Nearly 

 all specimens should be examined in a liquid. Water will 

 do for nearly all. Glycerine may be used if the specimen 

 is to be kept, for it does not evaporate. A drop is placed 

 over the specimen on the slide. Over the drop of liquid 

 it is well to place a thin piece of glass, called a cover glass, 

 for the purpose of protecting the objective from the 

 liquid, and the specimen from currents of air. Air bub- 

 bles under the cover glass interfere with the view. They 

 can be forced out by gently pressing upon the cover glass ; 

 but with care the cover glass can be applied so as to avoid 

 them. A supply of slides and cover glasses is a necessary 

 part of every microscopic outfit. 



A few fibers scraped off from a handkerchief or a few 

 scales from the back of the hand are good specimens for 



