STAINING OF TUBERCLE BACILLI IN TISSUES. 169 



immediately washed in water. Generally the red color 

 reappears and the section must be again subjected to the 

 action of the blue solution and again washed in water. 

 This must be repeated until the blue almost, if not quite 

 completely and permanently, replaces the red stain. This 

 is the most important part of the process and entirely 

 satisfactory results are only obtained after some practice. 

 The tendency is usually to not sufficiently replace the 

 fuchsin with the methyl-blue, and in consequence the 

 red color of the bacilli is masked by the red of the 

 surrounding tissues. Unless all acid is thoroughly 

 removed by the final washing in water the stain is not 

 permanent. The section is then completely dehydrated 

 with absolute alcohol, after taking up the excess of 

 water on the slide with blotting-paper. The alcohol is 

 followed by turpentine, and the process is completed by 

 mounting in xylol balsam. 



In case it is desired to stain sections cut by the 

 freezing method, they are placed upon a slide on which 

 a few drops of the gelatin fixative have been placed, and 

 after about five minutes, during which the fixative will 

 have penetrated the section, the surplus is poured from 

 beneath the section. The slides are then set aside for 

 the gelatin to harden by drying, and after drying they 

 are placed in bichromate fluid to render the gelatin 

 insoluble. They are then manipulated in exactly the 

 same manner as the sections cut by the paraffin method. 



This method gives equally good results with tissues 

 containing the lepra bacillus as with those containing 

 tubercle bacilli. 



