30 MANUAL OF BACTERIOLOGY. 



which aniline dyes operate may be increased by adding aniUne 

 oil to the solution : 



Aniline oil 5 ex. 



Water loo c.c. 



Mix, shake vigorously, filter; the fluid after filtration should 

 be perfectly clear; add — 



Alcohol lo c.c. 



Alcoholic solution of fuchsin (or gentian-violet, or 



methylene-blue) iic.c. 



Aniline-water staining solutions do not keep well, and need 

 to be freshly prepared about every two weeks. The applica- 

 tions of the anihne-water stains will be given under separate 

 headings. In general, however, they are employed where a 

 stain of unusual power is required. 



Gram's Method. — The advantages of Gram's method are 

 that by using it certain kinds of bacteria may be stained a violet 

 color, while other bacteria are stained feebly or not at all. Cover- 

 glass preparations, having been prepared and fixed in the usual 

 manner (see pages 26 and 27), are stained as follows: 



(a) Stain in aniline-water gentian-violet solution, from two to 

 five minutes. The intensity of the stain may be increased by 

 warming slightly. 



(6) Iodine solution, one and one-half minutes: 



Iodine i gram. 



Potassium iodide 2 grams. 



Water 300 c.c. 



In this solution the preparation becomes nearly black. 



(c) Wash in alcohol repeatedly; the alcohol becomes stained 

 with clouds of violet coloring matter; the alcohol is used as long 

 as the violet color continues to come away, and until the prep- 

 aration is decolorized or has only a faint steel-blue color. 



(d) When desired, the specimens may be stained, by way of 

 contrast, with a watery solution of Bismarck brown or eosin. 



