1 6 MEDICAL BACTERIOLOGY 



GENTIAN VIOLET 



Saturated alcoholic solution of gentian violet, 5 cc. 



Distilled water, 95 cc. 



Apply the same as Loeffler's methylene blue. 



EOSIN 



Eosin, J4 to y Gm. 

 Distilled water, 100 cc. 



Allow stain to remain on the specimen for i minute, then wash off with water. 

 Gram's method of staining permits the differentiation of organisms otherwise 

 indistinguishable under the microscope, and is, therefore, of great service. 



GRAM'S METHOD 



1. Stain specimen with anilin gentian violet for 3 to 5 minutes. 



2. Wash with water to remove excess stain. 



3. Apply Gram's solution for 2 minutes. 



4. Wash specimen with 95 per cent, alcohol until specimen gives off no more 

 color. 



5. Dry and examine. 



Gram positive bacteria (Gram +) remain a deep violet, almost black. 



Gram negative bacteria (Gram ) are colorless. 



When the anilin gentian violet is applied to a slide or cover glass, all the 

 bacteria on it are stained violet. When the alcohol is applied it does not affect 

 the Gram positive bacteria, they remain violet, but the alcohol takes the violet 

 stain out of the Gram negative bacteria, or in other words, decolorizes them. 



As unstained bacteria are almost indiscernible, a counter stain is usually 

 applied after staining by Gram's method. 



GRAM POSITIVE GRAM NEGATIVE 



Cocci 



Micro- 

 cocci 

 of 



Suppur- 

 ation 



Staphylococcus pycgenes albus 



Staphylococcus pyogenes aureus 



Staphylococcus pyogenes citreus 



Micrococcus pyogenes fcetidus Gonococcus 



Micrococcus cereus albus Meningococcus 



Micrococcus cereus flavus Micrococcus catarrhalis 



Micrococcus epidermidis albus Micrococcus melitensis 



Streptococci 



Pneumococci 



Sarcina lutea 



Sarcina alba 



Sarcina aurantiaca 

 Micrococcus tetragenus 



