160 Methods of Observing Bacteria 



in 0.5 to i per cent, acetic acid solution. The acid removes the 

 stain from the tissues, but ultimately from the bacteria as 

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

 color has almost disappeared from the sections, they must 

 be removed and transferred to absolute alcohol. At this 

 point the process may be interrupted to allow the tissue 

 elements to be countercolored 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. 



The greater number of applications can be made by 

 simply dropping the reagents upon the slide while held in 



the fingers. Where expos- 

 ure to the reagents is to be 

 prolonged, the Coplin jar 

 (Fig. 23) or some more 

 capacious device must be 

 employed. 



Pfeiffer's Method. The 

 sections are stained for one- 

 half hour in diluted Ziehl's 

 carbol-fuchsin (pp. 166 and 

 353), then transferred to 

 absolute alcohol made feeb- 

 ly acid with acetic acid. 

 The sections must be care- 

 fully watched, and so soon 

 as the original, almost 

 black-red color gives place to a red-violet color they are 

 removed to xylol, to be cleared preparatory to mounting 

 in balsam. 



Loffler's Method. Certain bacteria that do not permit 

 ready penetration by the dye require some more intense 

 stain. One of the best of these is Lofner's alkaline methy- 

 lene-blue : 



Saturated alcoholic solution of methylene-blue . . 30 

 1 : 10,000 aqueous solution of caustic potash . . 100 



The cut sections of tissue are stained for a few minutes 

 and then differentiated in a i per cent, solution of hydro- 

 chloric acid for a few seconds, after which they are dehy- 

 drated in alcohol, cleared in xylol, and mounted in balsam. 



CROSS-SECTION 

 SHOWING SLIDES 

 IN POSITION. 



Fig 2 3 .-Coplin's staining jar. 



