182 BACTERIOLOGY. 



recommended as a means of differentiation of organisms, 

 the differences claimed to be produced consisting of 

 alterations in the color of the media due to oxidizing or 

 reducing properties of the growing bacteria. As yet 

 but little has come from this method of work. It can- 

 not at present be recommended as a reliable means of 

 diagnosis. 



BEHAVIOR TOWARD STAINING REAGENTS. The 

 behavior of certain organisms toward the different dyes 

 and their reactions under special methods of after- 

 treatment serve as aids to their diagnosis. With very 

 few exceptions bacteria stain readily with the common 

 aniline dyes, but they differ materially in the tenacity 

 with which they retain these colors under the subsequent 

 treatment with decolorizing agents. 



The tubercle bacillus and the bacillus of leprosy, for 

 example, are difficult to stain, but when once stained 

 retain their color under the action of such energetic 

 decolorizing agents as alcohol, nitric acid, oxalic 

 acid, etc. 



Certain other organisms when stained with a solution 

 of gentian violet in aniline-water, retain their color when 

 treated with such decolorizing bodies as iodine solution 

 and alcohol (Gram's method), while again others are 

 completely decolorized by this method. 



Many of them can only be treated with water, or but 

 for a few seconds with alcohol, without losing their 

 color. 



It is essential that these peculiarities should be care- 

 fully noted in studying an organism. 



FERMENTATION. The production of gas as an in- 

 dication of fermentation is an accompaniment of the 

 growth of some organisms. This is best studied in 



