INTRODUCTION 13 



danger is avoided of accumulating errors which will injure 

 the image to an intolerable degree. When there is time and 

 opportunity, it seems advisable that the user of the micro- 

 scope should start with the lowest magnifications, and 

 proceed slowly through low and medium, before reaching 

 the high ones. Certain points have to be considered in 

 the training of the microscopist. Among these may be the 

 following: automatic movement of the slide in the right 

 direction; incessant use of the fine motion; solving the 

 cover-glass problem; learning the star test; movement of 

 the iris of the condenser only to regulate the aperture; 

 adjusting the condenser to the lamp distance ; learning the 

 ring test; constant use of light screens or yellow-green 

 light filters; use of small diaphragms on the source of 

 light; employment of the water-immersion objective with 

 a correction collar; and the use of dark-field condensers 

 of the highest aperture. A list of 62 causes of image 

 injury w-hich have attracted the writer's attention, in using 

 the monocular microscope, is also given. Rules for 

 optimum high-power microscopy are added. 



