TECHNICAL APPENDIX. 175 



(4) After-staining with methyl blue (a few sec- 

 onds). The spores remain red, the bacilli blue. 



6. Staining of Tubercle Bacilli. This is done ac- 

 cording to the same principles as the staining of 

 spores. The preparation is treated in the flame 

 with a deeply staining solution and then everything 

 with the exception of the tubercle bacilli is decolor- 

 ized with some acid solution. 



(a) We may manipulate exactly as in spore staining 

 (according to Ziehl-Neelsen), except that the prepara- 

 tion is drawn only three times through the flame. 

 This method is the only one employed by us. An- 

 other favorite method is the one recommended by A. 

 Fraenkel and Gabbet, in which decolorization and 

 after-staining are effected at the same time. Then 

 the preparation which has been stained with hot car- 

 bolized fuchsin, and washed in water, is placed in the 

 following solution: 



Sulphuric acid 1 



Distilled water 3 



Methyl blue, q.s. until the most intense blue color is pro- 

 duced. 



We then wash carefully in water, dry, and mount in 

 Canada balsam. 



However convenient this method may be, it is 

 better, for those who are not very experienced, to 

 stain, differentiate with acids, and after-stain sepa- 

 rately, because in this way success is more assured. 



(b) Ehrlich-Koch's method is also often employed. 

 The dry preparation is drawn through the flame, 

 treated with aniline gentian solution for one to two 

 minutes over the flame and heated with acid (usually 

 thirty per cent nitric acid) for one to four seconds, 



