QUESTIONS 27:? 



99. Why do feebly stained bacteria show the complementary color 

 with a dark field? 



100. What are the advantages of a dark field? 



101. How can the study of stained sections in balsam or immersion oil 

 best be supplemented? 



102. What are submicroscopic objects? 



103. What is the calculated limit of resolution? 



104. What is the limit of useful magnification? 



105. What arrangement is needed to examine stained bacteria di-y in 

 air? 



106. What use did Coles make of paraffin oil m the study of spiro- 

 cha^tes? 



107. Name six classes of objects, and the objectives most suitable for 

 their study. 



108. Why does not the 40 objective usually give, in unpractioed 

 hands, as sharp an image as the 10 objective? 



109. How nuich variation in cover-glass thickness obviously blurs 

 the image of the -iO objective, of 0.85 aperture? 



110. What variation in thickness is often met with in No. 1 co\'er- 

 glasses? 



111. Name seven solutions of the cover-glass problem. 



112. Which solutions are best (a) for routine laboratory work, and 

 (b) for research with high powers? 



113. Why are objectives of 50 or 25 millimeters usually unnecessary 

 on the routine and research microscopes for high-power work? 



114. How is a change of the bright-field condenser avoided on the 

 standard microscope when changing objectives? 



115. Why did Abbe state that the use of a 60 oil-immersion objective 

 of 1.3 or 1.4 aperture was a goal to be aimed at? 



116. How is the magnification of an objective reckoned in the modern 

 style? 



117. How is the magnification of an eyepiece now reckoned? 



118. Why is it good to designate both objectives and eyepieces by 

 their magnification numbers? 



119. What is the highest useful magnification of an objective i)lus 

 condenser? 



120. How is the highest allowable eyepiece magnification to lie 

 reckoned? 



121. Why is it better to buy a good condenser than another good 

 objective? 



122. What are the advantages of apochromatic objectives? 



123. How may an achromatic >i2 oil-immersion objective l)e made 

 nearly equal to an apochromatic? 



124. How can objectives be cared for? 



