86 STUDY OF BACTERIA 



forming, as it were, a double salt between the two. Certain sub- 

 stances, alkalies, carbolic acid, iron and copper sulphate, tannic 

 acid, alum, and aniline oil, are added to a solution of aniline dyes, 

 and they act as mordants, or fixatives, making the dye bite into the 

 protoplasm of the bacterial cells. Spores, capsules, and flagella, 

 are hard to stain, and special heavily mordanted stains are used to 

 demonstrate them. Chemical reaction occurring in the cell proto- 

 plasm is of great value in differentiating bacteria. The presence of 

 granules in bacterial cells is often only shown by the use of special 

 stains, which deeply color them. Bacteria of the tubercle group are 

 called "acid fast," because, after being stained, it is difficult to 

 decolorize them with acid solutions. These bacteria are hard to 

 stain and resist decolorizing agents after they are stained. 



1. Lb'ffler's alkaline methylene blue solution consists of 



Saturated alcoholic solution of methylene blue 30 c.c. 



YO^-Q solution caustic soda solution in water 100 c.c. 



Mix. 



This is the most useful of all the staining mixtures employed. 



2. Zeihl's solution carbol-fuchsin consists of 



Fuchsin i gram. 



Carbolic acid crystals 5 grams. 



Dissolved in 100 c.c. of water, to which is added 10 c.c. of absolute alcohol. 



This can also be made by taking a 5 percent solution of carbolic 

 acid in water and adding sufficient saturated solution of fuchsin in 

 water until a bronze scum persists upon the top. This is used for 

 staining tubercle bacilli in sputum and sections. It must be heated 

 when used for rapid staining. Tubercle bacilli can .be stained in 

 cold solution, if immersed over night in it. 



3. Fuchsin solution. 



Saturated alcoholic solution of basic fuchsin. . . i c.c. 



Water... 100 c.c. 



