TUBERCLE BACILLUS IN SECTIONS. 543 



in water and exposed to Lugol's iodine solution (p. 288), for 

 3 to 5 minutes. The specimens are then washed with water, 

 dried with filter-paper, and transferred to a mixture of -2 

 parts of xylol and 1 part of anilin. They remain in this 

 mixture till the color ceases to be given off, after which 

 they are again dried with paper, covered with Canada bal- 

 sam and examined. 



TUBERCLE BACILLUS. 



Thin sections made from tubercular human lung- and 

 from the spleen, liver and mesenteric tubercles of a guinea- 

 pig which received an intraperitoneal injection of tubercu- 

 lar sputum, are stained according to the following method, 

 which is a modification of the Ziehl-Neelsen process. The 

 sections, if very thin, should be fixed on cover-glasses 

 (p. 536). 



It may be well, first of all, to call attention to two con- 

 ditions which influence the staining of the tubercle bacillus. 

 In the first place, the bacillus loses its specific staining 

 power when the tissue has been kept in alcohol for some 

 time. This is equally true of the leprosy bacillus. It is 

 therefore advisable to use fresh tissues; or, as stated on p. 

 533, to preserve it in paraffin. Again, Ziehl's carbolic fuchsin 

 solution is not as permanent as it is commonly said to be. 

 In time, a tarry deposit forms in the bottle and the stain- 

 ing power of the liquid is materially decreased. A fresh 

 Ziehl solution should be prepared according to the direc- 

 tions given on p. 293. 



The section is floated on cold, fresh carbolic fuchsin over 

 night; or, for about -J- hour on a stain previously warmed to 

 about 40. The stain can be heated on an iron-plate as 

 shown in Fig. 22. It is then poured into a warm Petri dish. 

 The more deeply the section is stained the more difficult it 

 will be to properly decolor it. 



