10 INTRODUCTION 



Bacteria may be divided into two groups, viz.: 

 i. Those which stain by Gram's method (Gram positive, 4-) 

 . ii. Those which do not retain the gentian- 

 violet stain when washed a short 

 time with alcohol . . (Gram negative, - ) 



In using the test upon a doubtful organism of coccus form, it 

 is sometimes useful to mix the latter with a bacillus, such as 

 Bs. subtilis, known to stain by Gram's method ; or, if a bacillus 

 is to be tested, mix it with a Gram-staining coccus, such as 

 Str. lacticus. 



The following organisms are Gram positive : 

 Most species of Micrococcus. 



Sarcina. 



Bs. subtilis. 

 Bs. megatherium. 

 Bs. mesentericus. 

 Bs. mycoides. 

 B. (Proteus) mirabilis. 

 B. (Proteus} Zenkeri. 

 Bact. acidi lactici. 

 Str. lacticus. 

 Most yeasts and fungi. 

 The following are Gram negative : 



Most species of Spirillum. 

 Bact. coli. 



Bact. lactis aerogenes. 

 Bact. fluorescens. 

 Bact. prodigiosum. 

 Bact. pyocyaneum. 



Try Gram's stain upon a series of cover-glass films of 

 organisms obtained from the hay, cabbage, and pea extracts 

 of Exs. 3 and 4. 



