BACTERIOLOGICAL TECHNIQUE 19 



X. THE GRAM METHOD OF STAINING COVER-GLASS 



SPECIMENS. 



1. The 'fixed' cover-glass specimen is stained two to five minutes 

 with Ehrliclv's anilin water gentian violet (see 55). 



2. Wash with water. 



3. Differentiate with Gram's solution of iodine (see 60) until 

 the stained surface blackens like a tea-leaf which usually takes a 

 half to one minute. 



4. Decolorize with alcohol until no more stain comes away. 



5. Wash in water. 



6. Dry, and mount in xylol balsam. 



The Gram method is employed to differentiate Bacteria into two 

 divisions : 



(a) Those staining according to the method. 



(b) Those decolorized according to the method. 



According to Lehmann, recent researches show that the result 

 depends very much upon the age of the culture and condition of the 

 organism at the time the specimen is stained, as well as the method 

 employed. 



The Bacillus of Black Quarter, or ' Symptomatic Anthrax, 1 can also 

 be stained under certain circumstances, although most authors write 

 to the contrary. 



In order to check the Gram test and place results beyond doubt, 

 proceed as follows : 



Take a clean cover-glass and put a small quantity of the 

 material to be stained on one half, and on the other 

 half a small quantity of a young culture of Bacillus 

 anthracis. Air dry, fix, and stain by the ordinary Gram 

 method above mentioned, so that both materials on the 

 cover-glass are thus subject to the same reagents and 

 conditions. 



The Bacillus anthracis staining readily according to the Gram 

 method, one can thus judge whether the bacterial species under in- 

 vestigation stains or decolorizes by this method. 



XL THE FOLLOWING BACTERIA STAIN ACCORDING 

 TO THE GRAM METHOD. 



1. Bacillus anthracis. 



2. Bacillus of Tuberculosis. 



