50 BACTERIOLOGY FOR NURSES 



tiation. By its means organisms are divided into two classes : 

 those which retain the initial stain are spoken of as Gram positive 

 and those which are decolorized and take the counterstain as Gram 

 negative. Most bacteria fall decidedly into one class or the other ; 

 borderline cases do occur, however, and a few species show a tend- 

 ency to change from Gram positive to Gram negative in old cul- 

 tures. 



CLASSIFICATION OF THE PRINCIPAL PATHOGENIC BACTERIA ACCORDING 

 TO THEIR REACTION TO GRAM'S STAIN 



POSITIVE NEGATIVE 



(Retain the violet stain) (Take the counterstain) 



Cocci Cocci 



M. tetragenus M. catarrhalis 



Pneumococcus group M. gonorrheas 



Staphylococcus group M. meningitidis 



Streptococcus group M. melitensis 



Bacilli Bacilli 



B. serogenes capsulatus B. acidi lacti 



B. anthracis B. coli group 



B. botulinus B. dysenterise group 



B. diphtherise group B. enteritidis group 



B. tetani B. influenzas group 



B. tuberculosis and other acid- B. Koch- Weeks 



fast bacilli B. lactis aerogenes 



B. maligni edematis 



B. mallei 



B. Morax Axenfeld 



B. mucosus capsulatus 



B. pertussis group 



B. pestis 



B. proteus . 



B. pyocyaneus 



B. typhosus group 



Spirillum 

 S. choleras 



