4 APPARATUS 



After using the oil-immersion objective the lens should be wiped clean of oil 

 with a strip of Japanese lens paper or with a silk handkerchief. If the oil should 

 dry on the surface of the lens it may be removed with a drop^of xylol on a piece of 

 lens paper. Immediately afterward the lens should be dried. Dried oil on a lens 

 often causes the lens to be considered defective. Accidental contact of the dry 

 objectives with oil is not uncommon and should always be thought of when satis- 

 factory optical effects are not obtainable. 



It is advisable to cultivate the use of both eyes in doing microscopical work. 

 When using one eye the other should be kept open with accommodation relaxed. 

 It is this squinting of the unemployed eye which so often fatigues. A strip of card- 

 board 4 or 5 inches long, with an opening to fit over the tube of the microscope, 

 leaving the other end to block the vision of the unused eye, will prevent the strain. 

 This apparatus can be purchased in vulcanite. 



A warm stage for the study of living protozoa may be extemporized by taking 

 a piece of copper about the size of the stage and with a strip projecting out ante- 

 riorly for 5 or 6 inches. The under surface of the plate is covered with flannel and 

 a hole about i inch in diameter cut out of the center. The proper amount of heat 

 is applied by a flame impinging on the tongue-like projection of the copper plate. 



Direct sunlight or excessively bright light is to be avoided. If such conditions 

 must exist a white shade or muslin curtain drawn across the window is a necessity. 

 Light from the north and from a white cloud is the most desirable. South of the 

 equator a southern light. In the tropics a piece of plate glass fitted into the lower 

 part of a wire screen frame gives good lighting, keeps out dust, and does not interfere 

 greatly with the circulation of the air. 



The technic in connection with proper illumination is probably more important 

 than any other point; unless the light is utilized to the best advantage, the best re- 

 sults cannot be obtained. In examining fresh blood preparations or hanging drops 

 the concave mirror should be used and the light almost shut off by the iris dia- 

 phragm so as to give a contour picture. In examining a stained blood or bacterial 

 preparation, the Abbe condenser should be properly focused so as to best illuminate 

 the stained film. In many instruments set-screws are provided which check the 

 elevation of the Abbe condenser when the proper focus is reached. Inasmuch as 

 the light from the condenser should come to a focus exactly level with the object 

 studied, it is evident that a fixed position for the condenser would not answer when 

 slides of different thickness were used. Always use the plane mirror when examin- 

 ing stained bacterial or blood films, as a color image is desired. Ordinarily in ex- 

 amining tissue sections, the Abbe condenser should either be put out of focus by 

 racking down or by the use of the concave mirror and the narrowing of the aperture 

 of the iris diaphragm. Swing-out condensers are now made which are very con- 

 venient. The proper employment of illumination only comes with experience, and 

 one should continue to manipulate his mirrors, diaphragm, and condenser until 

 the best result is obtained. Then study the specimen. 



For microscopical work in a laboratory not properly supplied with windows or 

 for night work the frosted incandescent bulb is very satisfactory. 



Dark Ground Illumination. Very valuable information, especially 

 as regards the detection of treponemata in material from hard chancres 



