24 BACTERIOLOGICAL APPARATUS 
ble. The following pages have been prepared from a number of 
sourees. Direct reference has been given in a few cases. Most of the 
data, however, have been taken with permission from microscope 
manuals which are furnished by the Bausch & Lomb Optical and 
Spencer Lens Companies. 
Don'ts 
Don’t allow dust and dirt to settle on the microscope. 
Don’t carry the microscope by the arm, unless the fine adjustment 
is protected. 
Don’t use alcohol on the microscope. 
Don’t expect toe great a range in the fine adjustment. 
Don’t take the fine adjustment apart. 
Don’t bring the objective into contact with the cover glass. 
Don’t fail to focus up before turning the nosepiece unless you know 
the objectives are parfocal. 
Don’t forget that high powers have short working distances. 
Don’t focus down with the eye at the eyepiece. 
Don’t fail to secure good even illumination. 
Don’t drop the objectives and oculars. 
Don’t try to take an objective apart. 
Don’t try to clean the lens with a dirty cloth. 
Don’t fail to clean oil from an immersion lens immediately after 
using. 
Don’t try to work with:an immersion lens when there are air bubbles 
in the oil. 
Don’t use high powers when low ones will do. 
Don’t use higher oculars than necessary. 
Don’t expect a lens to work at its best unless used on a cover thick- 
ness, and with a tube length, for which it is corrected. 
Don’t shut one eye. 
Don’t get discouraged if desired results do not come immediately. 
The instrument should always be kept in a case, either the one 
in which it was received from the factory or one which is specially 
constructed to hold a series of them in the laboratory. When carry- 
ing a microscope or removing it from its case, grasp it by the pillar 
and not by any other part. 
Finger marks and stains should be carefully rubbed with soft cloth 
or lens paper. If this is not sufficient, a little ether, chloroform or 
xylol may be used. Alcohol should never be used since this will remove 
the lacquer. 
