96 PATHOGENIC BACTERIA. 



cent, solution of hydrochloric acid for a few seconds. 

 The section is subsequently dehydrated in alcohol, cleared 

 up in xylol, and mounted in balsam. 



Pfeiffer's Method. The sections are stained for one- 

 half hour in diluted ZiehPs carbol-fuch^in (q. v.\ then 

 transferred to absolute alcohol made feebly acid with 

 acetic acid. The sections must be carefully watched, 

 and as soon as the original, almost black-red color gives 

 place to a red violet color the section is removed to 

 xylol, where it is cleared preparatory to mounting in 

 balsam. 



For ordinary work the following simple method is 

 recommended: After the sections are cut the paraffin 

 must be, and the celloidin had better be, removed. 

 From water the sections are placed in the same watery 

 stain used for cover-glasses and allowed to remain five 

 to eight minutes. They are next washed in water for 

 several minutes, then decolorized in 0.5-1 per cent, 

 acetic-acid solution. The acid removes the stain from 

 the tissues, and ultimately from the bacteria as well, 

 so that one must watch carefully, and as soon as the 

 color almost disappears from the sections remove them 

 to absolute alcohol. At this point the process may be 

 interrupted to allow the tissue-elements to be counter- 

 stained with alum carmin or any stain not requiring 

 acid for differentiation, after which the sections are 

 dehydrated in absolute alcohol, cleared in xylol, and 

 mounted in Canada balsam. 



fa will be mentioned hereafter, certain of the bacteria 

 which occur in tissue do not allow of the ready penetra- 

 tion of the color. For such forms a more intense stain 

 must l>t- employed. One of the best of these stains, 

 which can be employed by the given method both for 

 cover-glasses and tissues, is Loffler's alkaline methylene 

 blue : 



Saturated alcoholic solution of methylene blue, 30 ; 

 i : 10,000 aqueous solution of caustic potash, 100. 



