46 BACTERIOLOGY 



(e) Wash in water, and examine either in water directly or 

 after drying and mounting in Canada balsam. Gram's method 

 and its modifications should not be regarded as absolute means 

 of distinguishing between Gram-positive and Gram-negative bac- 

 teria in every case, as much depends upon the condition of the 

 bacteria, and very much upon the technic of staining. When the 

 Gram stain is used for diagnosis, it is well to put a smear of a 

 known Gram-negative and a smear of a known Gram-positive 

 organism on the same slide or cover-glass along with the un- 

 known, and subject them all to the same technic. 

 Some bacteria that are stained by Gram's method : 



Staphylococcus aureus, 



Streptococcus pyogenes. 



Micrococcus lanceolatus (of pneumonia), 



Micrococcus tetragenus, 



Bacillus of diphtheria, 



Bacillus of tuberculosis. 



Bacillus of leprosy. 



Bacillus of anthrax, 



Bacillus of tetanus. 



Bacillus welchii (aerogenes capsulatus), 



Ray fungus of actinomycosis. 

 Of these the tubercle bacillus and the bacillus of leprosy 

 require a much longer exposure to the stain than other bacteria 

 in the list. 



Some bacteria that are not stained by Gram's method : 



Gonococcus, 



Diplococcus intracellularis (meningitidis) , 



Micrococcus melitensis, 



Bacillus of chancroids (Ducrey), 



Bacillus of dysentery (Shiga), 



Bacillus of typhoid fever 



Bacillus coli, 



BacUlus pyocyaneus. 



Bacillus of influenza, 



