THE MICROSCOPE. 41 



c. Arrange the mirror and illuminate the field of vision ; 

 use a small aperture of the diaphragm in the case of a high 

 power. If any specks be visible on looking through the 

 microscope, they are upon either the upper or lower glass 

 of the eyepiece (probably on the upper surface of the 

 latter), and must be removed. Muscat volitantes must not 

 be mistaken for such specks. The latter move as the eye 

 changes its position. Dirt upon the objective is indicated 

 by no definite forms on looking through the microscope, but 

 by a dimness of the object which may be under examination. 



d. Clean one or more cover-glasses. If the glass be 

 new, use dilute alcohol. The cover-glass ought never to be 

 laid flat upon the table, but should always be tilted on edge 

 against some suitable support until required ; otherwise, the 

 surface to be applied to the object will be contaminated 

 with various particles. 



56. Preparation of a Simple Object. Place a small 

 drop of milk upon the centre of a slide. Hold the cover- 

 glass by the margin, between the thumb and forefinger ; 

 rest the free margin nearest the finger-tips upon the slide, 

 and allow the glass to fall, in this oblique manner, gently 

 upon the object. If the cover-glass be perfectly clean the 

 fluid will meet its surface evenly, if not, unmoistened 

 islands will be left, and air thus entangled. -By gently 

 raising the margin of the cover-glass with a needle once or 

 twice the air-bubbles may be got rid of. If too much fluid 

 has been taken, remove it from the margin of the cover 

 with bibulous paper. 



In mounting speci- 

 mens it is very important 

 to allow the cover-glass 

 to fall evenly, and with- 

 out shifting its place, on 

 the slide. This is best 



done with a pair of for- FIG. 37. Application of the cover-glass. 



ceps (Fig. 37). 



57. Description of the Object It is very important 

 that the student should be educated in the method of 

 describing microscopic objects. To facilitate description, 

 he should attend to the following : 



