140 



ELEMENTARY CHEMICAL MICROSCOPY 



By means of the mechanical stage the investigator is enabled 

 to search systematically the entire area of a preparation in such 

 a manner as to ensure that no portion has been missed, nor has 



FIG. 71. Removable Mechanical Stage. Spencer Lens Co. 



any portion been twice examined, a matter of vital importance 

 in quantitative work, in clinical microscopy and in the examina- 

 tion of foods for adulteration. 



Before attaching a mechanical stage of this type to the micro- 

 scope, first lay a thin card or a piece of thick paper upon the stage 

 of the microscope, then lay the mechanical stage upon the paper 

 and securely clamp it in place about the base of the pillar of the 

 microscope. Pull out the card or paper and the stage is ready 

 for use. The card or paper has as its function preventing the 

 arms from rubbing upon the stage when the arms of the mechan- 

 ical stage are moved. Unless a tiny space is left between the 

 microscope stage and the mechanical stage, a free and smooth 

 movement of the preparation back and forth beneath the objec- 

 tive may be seriously hampered. 



