158 PATHOGENIC BACTERIA. 



counter-stained with a watery solution of vesuvin, chrys- 

 oidin, methyl blue, malachite green, or safranin, according 

 to the color of the preceding stain. This whole process 

 is said to take only from eight to ten minutes, and to give 

 remarkably clear and beautiful pictures." 



Method of Staining Flagella. — This is much more 

 difficult than the staining of either the bacteria or their 

 spores, because each species seems to behave differently 

 in its relation to the stain, so that the chemistry of the 

 micro-organismal products must be taken into considera- 

 tion. 



The best method introduced is that of Loffler. 1 In it 

 three solutions are used : 



A. A 20 per cent, solution of tannic acid, 10 ; 

 Cold saturated aqueous solution of ferrous sulphate, 5 ; 

 Alcoholic solution of fuchsin or methyl violet, 1. 



B. A 1 per cent, solution of caustic soda. 



C. An aqueous solution of sulphuric acid of such strength 



that 1 c.cm. will exactly neutralize an equal quan- 

 tity of Solution B. 



Some of the bacteria to be stained are mixed upon a 

 cover-glass with a drop of distilled water. This is the 

 first dilution, but is too rich in bacteria to allow the 

 flagella to show well, so that it is recommended to prepare 

 a second dilution by placing a small drop of distilled 

 water upon a cover and taking a small portion from the 

 first cover to the second, spreading it over the entire sur- 

 face. The material is allowed to dry, and is then fixed 

 by passing it three times through the flame. When this 

 is done with forceps there is some danger of the prepara- 

 tion becoming too hot, so Loffler recommends that the 

 glass be held in the fingers while the passes through the 

 flame are made. 



The cover-glass is now held in forceps, and the mordant, 

 Solution A, is dropped upon it until it is well covered. 



1 Centralbl.f. Bakt. u. Parasitenk., 1890, Bd. vii., p. 625. 



