GRAM'S DECOLORISING METHOD 77 



The preparation is next laid for 1 to 2 minutes in the 

 iodine and potassium iodide solution and transferred from 

 that into absolute alcohol, in which it remains until the 

 colour is discharged. The bacteria come out stained with 

 gentian violet, and the tissue may be double-stained red 

 with picrocarmine, Magdala red, or other dyes. 



Gram's method can be used as an aid to the diagnosis 

 of the vast majority of micro-organisms. For example, 

 the Pneumococcus Friedldnder shows no staining after going 

 through the process, and similarly the bacilli of Cholera 

 Asiatica, typhoid fever and glanders, gonococci, the spirilla 

 of recurrent fever, &c., cannot retain the colouring matter, 

 but give it up, as do also the nuclei of cells, when iodine 

 solution is applied. 



It is strongly to be recommended that the preparation 

 should not be brought directly from the staining fluid into 

 the iodine and potassium iodide, but be first rinsed free 

 of superfluous stain in plain aniline water before being 

 transferred to the iodine solution (Botkin) . 



In staining sections of tissue it is advisable to carry 

 out the ground staining before that of the bacteria, which 

 is done by immersing the sections in picrocarmine for one 

 or two minutes, washing in water, transferring to alcohol, 

 and then subjecting to Gram's process. 



Every pigment is not, however, suitable for this method, 

 since Unna has shown that it gives no results if fuchsine, 

 methyl blue, or Bismarck brown are used. The process 

 can only be carried out with the pararosanilines (methyl 

 violet, gentian violet, and Victoria blue). 



Gunther's modification of Grain's process. Not only pure 

 alcohol, but also alcohol to which 3 per cent, of hydrochloric 

 acid has been added, is used for decolorising. The cover- 

 glass or section of tissue is left for about two minutes in 

 aniline water gentian violet, but in the case of tubercle 



