62 GENERAL BACTERIOLOGY 



h. Mount in water and examine. 



i. Dry and mount in balsam. 



REFERENCES. A. 169 ; H. 89 ; M. & B. 102 ; McF. 150 ; P. 203. 



SPECIAL DIRECTIONS. Stain films of young cultures of B. coli 

 and B. subtilis. 



EXERCISE 36. TUBERCLE STAIN (GABBETT). 



EXPLANATORY. All of the differential methods of staining the 

 tubercle bacterium depend upon the fact that this germ is very 

 resistant towards the ordinary stains, and, in order to be stained at 

 all must be treated with a dye containing a mordant and this either 

 allowed to remain in contact with the micro-organism several hours 

 or be applied hot. The latter method is the quicker and is usually 

 employed, although it does not give as good results. When once 

 stained this germ withstands the effect of decolorizing agents to 

 such an extent that it is possible to remove the dye from all other 

 objects on the cover-glass preparation (as in sputum) while it retains 

 its own color. The application of a second dye, of a complementary 

 color, readily distinguishes this germ from all others in the field. A 

 few other bacteria have similar staining qualities. Red is the usual 

 stain and blue the counter stain. Gabbett's method is one of the 

 simplest. 



GENERAL DIRECTIONS. 



a. Spread film (sputum from tuberculous patient). 



fe. Air dry and fix. 



c. Stain with hot carbol-fuchsin 2 minutes. 



d. Wash in water. 



e. Treat with Gabbett's solution % to 1 minute. 

 /. Wash in water and examine. 



g. Dry and mount in balsam. 



REFERENCES. A. 167 ; H. 244 ; M. & R. 104 ; McF. 308 ; P. 304. 



SPECIAL DIRECTIONS. Stain three samples of sputa which con- 

 tain varying numbers of the tubercle bacteria. 



