106 STAINING OF BACTERIA 



the flame. This step is called fixing the cover-glass. By exposing 

 the dried pus, containing the dried bacteria, to the heat of the flame, 

 the proteids (albumins) are coagulated, and the spread, with its pus 

 corpuscles, bacteria, etc., now adheres firmly to the cover-glass. 



5. With the cover-glass still held in the forceps, stain for a few 

 minutes with one of the above watery anilin solutions by pouring 

 the stain on the air-dried fixed cover-glass. 



6. Wash well in water by moving the cover-glass about in the fluid. 

 Then drop it on filter paper and dry by pressing another piece of 

 filter paper over it. Mount on a slide in Canada balsam and 

 examine first with a low-power lens, then with the y 1 ^ inch (2 mm.) 

 homogeneous oil-immersion lens. To mount a preparation, put the 

 Canada balsam on the slide and drop the cover-glass, prepared side 

 down, on the balsam, then press the cover-glass down. 



If a bacterial cover-glass preparation from a pure culture is to be 

 examined the first steps in the preparation are as follows: 



1. Clean the cover-glass. Hold it in a Stewart forceps, and with a 

 sterile platinum loop place a small drop of water on the centre. 



2. Hold an agar or gelatin culture tube in an oblique position 

 between the index and middle fingers of the left hand. Remove the 

 cotton plug and hold it between the middle and fourth fingers of the 

 left hand. Now remove from the open culture tube with the sterile 

 platinum loop a very small amount of the bacterial growth from the 

 surface of the culture medium. Rub up with the platinum loop the 

 growth obtained with the drop of water on the cover-glass, so that 

 an even emulsion of the bacteria is formed. , 



3. Allow the cover-glass to become air dry. This may be hastened, 

 if desired, by moving it rapidly above the flame. When dry, fix 

 stain, wash, and mount as above. 



Precautions in Working with Pathogenic Bacteria. In working with 

 live, highly pathogenic bacteria, as, for instance, glanders, anthrax, 

 tetanus, etc., the following precautions should be strictly observed 

 in making stained cover-glass preparations : 



1. Have on the table, within easy reach of the student, a large 

 china or glass vessel (wooden or non-enamelled metal vessel will not 

 do) filled with a strong solution of bichloride of mercury (corrosive 

 sublimate) at least 1 to 1000, better still stronger. 



2. When making the cover-glass preparations be careful not to 

 contaminate anything; sterilize the platinum loop well before laying it 

 down. Never hold the culture tube so that the condensed water or 

 the bouillon can run out and soil the hands, table, cotton plug, or 

 anything else. 



3. Pour the stain carefully on the cover-glass, so that none of it 

 runs over. If it did so some dangerous pathogenic bacteria might 

 be washed down on the table. 



4. After the stain has acted long enough, pour it into the vessel 

 containing the bichloride solution. In washing a dangerous prepara- 



