SPECIAL METHODS. 433 



use the high power for the detection of red blood-corpuscles, pus, 

 etc. Objects in urinary sediments may be stained with aqueous 

 methylene-blue, Gram's solution of iodine, or alum-carmine; or 

 their chemical nature determined by means of microchemical reac- 

 tions. 



2. Preparation of Cover-glass Smears. These are used for the 

 examination of blood, pus, sputa, cultures of bacteria, etc., when it 

 is desired to employ stains. They are also employed occasionally 

 for the study of some of the constituents of soft tissues. 



A small drop, or fragment, of the specimen is placed between 

 two cover-glasses. If the specimen is sufficiently fluid, it will at 

 once spread out into a thin layer between the covers. When this 

 is not the case pressure may be used. The covers are then drawn 

 apart, not lifted, leaving a coating upon both. They are allowed to 

 dry spontaneously, after which the film is fixed by passing the 

 cover-glasses three times through a flame, care being taken not to 

 scorch the film, which should not come in contact with the flame. 

 Heat applied through the glass to the dry film will render it insol- 

 uble and affix it to the cover. The constituents of the film may 

 then be stained on the cover-glass, the latter being either floated 

 on the dye or immersed in it as though it were a section. Hsema- 

 toxylin and eosin may be employed ; but anilin-dyes, such as meth- 

 ylene-blue, carbol-fuchsin, anilin-gentian- violet, etc., are more com- 

 monly used. 



3. Examination of Sputa for Tubercle Bacilli. The small cheesy 

 particles in the sputa are most likely to contain tubercle bacilli. 

 Cover-glass smears are stained by the following method : 



a. Stain fifteen minutes in freshly filtered carbol-fuchsin at the 

 room-temperature, or heat until vapors rise from the surface of the 

 dye, and maintain that temperature for about three minutes. 



6. Wash off the excess of dye with water. 



c. Differentiate in dilute sulphuric acid, prepared by adding 5 cc. 

 of pure acid to 95 cc. of distilled water, until the cover-glass has 

 only a faint tinge of pink when the acid is washed off* with water. 



d. Wash in water to remove the acid. 



e. Counterstain with aqueous methylene-blue for two minutes. 

 /. Wash in water. 



g. Dry the cover-glass and mount it, film side down, on a drop 

 of xylol-dammar. 



The tubercle bacilli will be stained red, while other bacteria and* 



28 



