18 OMENTAL PLAGUE chap. 



from very long experience I consider as perfectly reliable 

 for obtaining the necessary result. 



Film specimens fixed in the flame are placed in absolute 

 alcohol for £ to 1 minute, then are placed, film downwards, 

 on gentian violet aniline water contained in a watch-glass ; 

 after one minute they are removed, well drained with 

 blotting-paper, and then transferred to Gram solution 

 (iodine dissolved in iodide of potassium), where they 

 remain for two minutes ; they are then transferred to 

 two successive lots of absolute alcohol, in each being 

 washed for a few (two to five) seconds, then well washed 

 in water, dried, and mounted. Gram-positive bacteria, 

 like B. anthracis, B. diphtheria, Staphylococcus aureus, 

 and others, appear of a deep-violet — almost black-violet 

 colour ; Gram-negative bacteria, like those of the coli- 

 typhoid group, proteus, gonococcus, B. pestis, are dis- 

 coloured, in fact are not stained. A good result is 

 obtained by using Gordon's modification, particularly when 

 the material contains, or is supposed to contain, a mixture 

 of Gram-positive and Gram-negative bacteria. 



This method is as follows : — The Gram staining is made 

 in the same manner as above, with this difference, that the 

 specimens remain in the gentian violet f to 1 minute, in 

 the Gram solution for the same time (f to 1 minute), and 

 after washing in alcohol, and then in water, are placed in 

 0*5 p.c. watery fuchsin solution for five to ten seconds, then 

 washed in water, dried, and mounted. The result is that 

 the Gram-positive bacteria, having retained the gentian 

 violet stain, appear violet black, whereas the Gram-negative 

 bacteria, having lost the first stain by the Gram solution, 

 have taken up the second, viz. the fuchsin stain, and 

 therefore appear bright pink. Film specimens of pus of a 



