STAINING OF BACTERIA IN TISSUES. 145 



They are known as " clearing fluids," and fill up the 

 gap that would otherwise be left in the process, for a 

 section caunot be mounted in balsam directly from alco- 

 hol ; the two bodies do not mix perfectly. 



A number of clearing agents are in general use ; in 

 fact, almost all the essential oils come under this head. 

 There is one oil of cloves which is very commonly 

 used in histological work, but it must not be employed 

 in tissues containing bacteria. It not only extracts too 

 much color from the bacteria, but causes them to fade 

 after the sections have been mounted for a time. 



When the section thus stained and mounted is ex- 

 amined microscopically, it may be found that the tissues 

 still possess so much color that the bacteria are not 

 visible, in which case they have not been decolorized 

 sufficiently ; or, on the other hand, both bacteria and 

 tissues may have parted with their stains then decol- 

 orization has been carried too far. In either case the 

 fault must be remedied in the manipulation of the next 

 section to be mounted. 



In short, the steps in the process of staining sections 

 in general are these : 



a. From alcohol into distilled water for one minute. 



6. Into the staining fluid for from five to eight 

 minutes. 



c. Into water for from three to five minutes. 



d. Into 0.1 per cent, acetic acid for about one-half 

 minute. 



e. Absolute alcohol for a few seconds. 

 /. Absolute alcohol for a few seconds. 

 g. Xylol for about one-half minute. 



h. Removal with spatula or section-lifter to slide. 

 i. Removal of excess of xylol. 

 j. Mounting in xylol-balsam. 



