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. 
