38 PRACTICAL BACTERIOLOGY 



4. Remove superfluous stain with filter-paper, wash the section 

 three times with 3 per cent, acetic acid, and do not allow the acid to 

 act for more than ten seconds each time. 



5. Remove all traces of the acid with distilled water, absorb the 

 water with filter-paper. 



6. Dry the section with gentle heat according to the dry method 

 of Unna (see 46). Clear in xylol, and mount in xylol balsam. 



XLV. KUHNE'S METHYLENE BLUE METHOD FOR 

 STAINING SECTIONS. 



1. Bring the sections out of alcohol into Kuhne^s methylene blue 

 (see 56) from a half to one hour (leprosy sections remain longer). 



2. Wash quickly in water. 



3. Wash in water containing 1'5 to per cent, hydrochloric acid 

 until the section becomes light blue in colour. 



4. Transfer the section to a solution of lithium carbonate, prepared 

 as follows : 



Concentrated watery solution of carbonate of lithia, 68 drops. 

 Water 10 c. c. 



5. Place the section in clean water three to five minutes. 



6. Immerse the section for a short time in absolute alcohol, to 

 which a little methylene blue in substance is added. 



7. Rinse the section completely in pure anilin oil. 



8. Place the section in thymol or oil of turpentine for two 

 minutes. 



9. Place in xylol. 



10. Mount in xylol balsam. 



The advantages of this method are that the bacteria are not 

 decolorized, whereas the tissues are sufficiently so to render the 

 bacteria visible, and admit of the use of contrast stains. 



XLVI. UNNA'S <DRY r METHOD 1 FOR SECTIONS. 



Many bacteria during the washing process become entirely de- 

 colorized, and to prevent this result the dry method of Unna is 

 employed as follows : 



1. The section is removed from the staining solution directly 

 into water. 



2. Spread the section out on a slide, and remove excess of water 

 with filter-paper. 



