iNTnonrcnox 5 



live, (c) The cover-glass on tlie slide is measured with tlie 

 graduated fine motion. (/) The upper surface of the cover 

 is freed from grease. (</) Water is run between the sHde 

 and the condenser, {h) The 10 objective is focused on the 

 object, as is also the condenser, (i) The iris of the condenser 

 is arranged to give about a nine-tenths cone, or less, for this 

 objective. (/) When a cell is found for examination by the 

 high power, the 3-millimeter diaphragm is placed close to the 

 ground glass, and centered by the prism, {k) The water- 

 immersion objective 70 is turned on, and the condenser 

 opened to give a Jio cone, or less, for this objective, after 

 refocusing. (/) The correction collar is first set for the 

 known thickness of the cover, and variations tried each way. 

 (w) If there is too intense a light, a denser green glass is 

 inserted in the holder. Critical observations can now be 

 made. If the preparation is mounted in immersion oil (or 

 balsam), / and I are omitted, since an oil-immersion 

 objective is to be employed. 



The effects of disregarding all the rules, and of attending 

 to all of them, are given in the following two columns. 



Rules Nearly All Disregarded Rules Nearly All Attended To 



1. The 5-times eyepiece gives the The 15- (or 20-) times eyepiece gives 



best images and is mostly the best images, and is usually 

 used. employed. 



2. The high dry objective gives The high dry objective gives sharp, 



hazy or foggy images. bright images. 



3. Glare prevents any approach to A %o cone is constantly employed 



a %o condenser cone. on stained objects. 



4. The H2 oil-immersion objective The 3-12 oil-immersion objective (of 



(of 1.3 aperture) will have a 1.3 aperture) will have a maximum 



maximum useful magnification useful magnification (without 



(without glare) of about 800. glare) of about 1,250. 



5. The smallest separable distance The smallest separable distance is 



is about 0.33 micron, with a 3- near 0.22 micron, with a 3-milli- 

 millimeter source, for the H2 meter source, for the if2 objective, 

 objective, without special 

 methods being used, such as 

 oblique light. 



6. The high-power objectives do The highest objective is as well illu- 



not get enough hght. minated as the lowest. 



7. The field of view shows curva- The field of view is nearly flat, 



ture, because of the low eye- because of the high eyepiece, 

 piece. 



