100 STUDY OF BACTERIA 



now used. If the bacteria on examination remain a dark violet- 

 blue they are then said to stain by Gram's method, or are " Gram- 

 positive." If they are decolorized they take the contrast stain and 

 are said not to stain by this method, and are "Gram-negative. " 



Many bacteria stain in this way, and many do not. Important 

 bacteria often may be differentiated in this manner. 



Examples of Gram's stain are as follows: 



Gram-positive Bact. aero genus capsulatus, Bact. anthracis, 

 Bact. diphtheria, B. tetani, Bact. tuberculosis, Streptococcus 

 pneumonia, Staph. pyogenes, Strep, pyogenes. Gram-negative 

 B. coli, B. dysenteries, Bact. influenza, Bact. mallei, Bact. pestis, 

 B. pyocyaneus, B. typhosus, Diplococcus intracellularis menin- 

 gitidis, Micr. catarrhalis, Micr. gonorrhoea, Spirillum cholera. 



Thionin Blue, or Carbol Thionin 



This is a useful stain, prepared thus: 



Thionin blue i gram. 



Carbolic acid ! 2.5 grams. 



Water 100 c.c. 



Filter. Good for staining bacteria in tissues. 



Special Stains 



Wright's Stain. This not only stains, but fixes. It has a wide 

 range of usefulness in a bacteriological laboratory for the staining 

 of blood, pus, malarial parasites, trypanosomes, as well as many 

 bacteria, and is prepared as follows : 



.5 percent solution of sodium bicarbonate 100 c.c. 



Methylene blue i gram. 



Mix and heat in sterilizer one hour at iooC. Cool, filter, then mix Ko per- 

 cent yellowish eosin in water until the mixture loses its blue color and becomes 

 purplish. Of the eosin solution add 500 c.c. to each 100 c.c. of the methylene 

 blue mixture. Mix and collect the abundant precipitate which immediately 

 forms on a filter. Dry this and dissolve in methyl alcohol in the proportion 

 of i gram of powder to 600 c.c. of the alcohol. This is the staining fluid. 

 Keep well stoppered. Fresh alcohol may be added for that which evaporates. 



