EXAMINATION OF BACTERIA WITH THE MICROSCOPE. 35 



The method given below is the one recommended. 

 Method for staining the tubercle bacillus : 



(a) The cover-glass preparation is made, dried and fixed by 

 passing through the flames three times (see pages 26 and 27). 



(b) The cover-glass, held in forceps or in a watch-crystal, is 

 covered with carbol-fuchsin and heated till bubbles begin to 

 appear showing that the water in the stain is boiling. The 

 stain should be allowed to act for- five minutes and kept hot 

 during this time. It is not always necessary to heat as high as 

 this nor to allow the stain to remain for so long a time; but in 

 order to be sure in all cases it is best to do so. 



(c) Wash in water. 



(d) Wash in alcohol containing 3 per cent, of hydrochloric 

 acid one minute, or longer if necessary to remove the red color. 



(e) Wash in water. 



(/) Stain with methylene-blue solution (see page 30) thirty 

 seconds. 



(g) Wash in water. 



It may be found necessary to repeat the treatment with 

 acid alcohol, and this should be done if the color returns to the 

 preparation after washing in water. 



(h) Examine in water directly, or after drying and mounting 

 in Canada balsam. 'Tubercle bacilli take a brilliant red 

 color; other bacteria and the nuclei of cells are stained 

 blue. 



Gabbett's Method. This method is very popular and widely 

 used on account of its convenience. It is not as reliable as the 

 one just given. 



Gabbett's solution : 



Methylene-blue i to 2 grams. 



25 per cent, watery solution of sulphuric acid 100 c.c. 



(a) The cover-glass preparation is to be made, dried and 

 fixed by passing through the flame three times. 



