THE COMl'orSI) MKUOSCOFE AM) ITS ISK :\7 



iiicnt, those who ;ii(' proficient in its use iii.iy turn iiiniiediately 

 to the study of the celluliir structure of the fro^. iV» om' should 

 aUeiupt to .study with the microscope before beiiiK able first to focUH 

 on an object with the h)\v-power objective and then change to the 

 high power and find the object without allowing; the high objec- 

 tive to come in contact with the cover sUp on the shde. Touch 

 only vietal parts. Consult Fig. 2 of a compound microscope and 

 identify the base, piUar, stage, handle arm, body tube, coarse 

 and fine adjustments, nosepiece, objectives, oculars, iris dia- 

 phrji^m, and mirror. 



In using the instrument, light is reflected from the movable 

 mirror through the aperture of the diaphragm in the stage, upon 

 which is placed the object to be examined. The observer looks 

 through the body tube to which the ocular and objectives are 

 attached. The revolving nosepiece at the lower end of the tube 

 holds the objectives of different powers and facilitates the change 

 from one to the other by turning upon its axis. It is, therefore, 

 unnecessary to remove an objective from its attachment to the 

 nosepieces. 



Always work with the low-power objective and ocular first. 

 These will soon be learned by the size and number. Place a 

 prepared slide of a wing of the house fly upon the stage, center 

 the light with the mirror, and by means of the coarse adjustment 

 bring the low-pow-er objective one-fourth inch above the slide. 

 Then, looking into the ocular, focus the microscope by gradually 

 raising the lens, using the coarse adjustment, and turning counter- 

 clockwise with the right hand until the object is brought into 

 view. The focus may then be sharpened by the use of the fine 

 adjustment. Compare the orientation of object and image. 



Note carefully the brightness of the field of vision and the 

 appearance of the object; it is illuminated by transmitted light, 

 i.e., light which is reflected from the mirror and passes through 

 the object. Tilt or cover the mirror and observe the change 

 in the intensity and character of the light. The object is now 

 viewed by reflected light, i.e., light which is reflected from the 

 surface of the object. Reflected light must be employed for all 

 opaque objects. 



In order to use the high-power objective, first place the slide 

 so that the object appears exactly in the center of the field as 

 viewed with the low-power objective; tiien increase the light and 

 change to the high-power objective by revolving the nosepiece 



