192 



done to remove the excess of dye and to differentiate the 

 bacteria in the tissue. From the decolorizing solution the 

 section is transferred to water then, by means of a spa- 

 tula, to a glass slide and examined with a No. 7 objective. 

 If the section is still too intensely stained it should be re- 

 turned to the decolorizing agent and after a while again 

 examined. When satisfactorily stained the sections should 

 be placed in absolute alcohol, for a few seconds, till 

 thoroughly dehydrated, they are then cleared up in oil of 

 cloves, cedar or anise; placed in xylol and examined on 

 a slide. If satisfactory the cover-glass is carefully lifted 

 off and the xylol removed from the section by means of a 

 piece of filter paper. A drop of Canada balsam is then 

 applied to the section and the whole covered with a clean 

 cover-glass. The exposure to absolute alcohol and to oil 

 of cloves should be carefully watched as both tend to re- 

 move the stain. The oil of cloves can indeed be relied 

 upon to remove any excess of dye that may be present. 



Instead of the ordinary dilute anilin stain, Lo (Tier's 

 methylene blue (page 140) or ZiehFs carbolic fuchsine 

 (page 110) can be employed in special cases to excellent 

 advantage. A dilute ZiehTs solution gives particularly 

 good results. The sections remain in this for about half an. 

 hour and are then transferred to absolute alcohol which is 

 very slightly acidulated with acetic acid. As soon as the 

 color changes to a peculiar reddish violet tint the section 

 is removed, cleared up in xylol, examined and mounted in 

 balsam. (Pfeiffer's method.) 



Double stain Gramas method. Those microorgan- 

 isms which can be stained by this method can be readily 

 detected in sections, as the preparations when properly 

 made show the heavily stained violet bacilli on a light pink 

 background. The student should begin with sections of 

 the kidney of the anthrax guinea-pig. A strong solution 

 of anilin water gentian violet is prepared according to the 

 directions given on page 106. It should be warmed slightly 

 on the radiator, or on an iron plate. The sections are placed 



