66 SPIROCILETES. 



are then washed in pyridine (10 per cent.) ; and reduc- 

 tion is effected by a fluid containing pyrogallic acid, 

 4 per cent., 10 per cent, acetone, and 15 per cent, 

 pyridine in distilled water. 



Ravaut and Ponselle use an albuminate of silver 

 ("largine") in 2 per cent, solution, followed by 5 per 

 cent, pyrogallic acid ; the largine bath may be repeated 

 a second time after the pyrogallic solution, the tissue 

 being washed with distilled water between the two baths. 



Yamamoto uses a 5 per cent, solution of silver ni- 

 trate, followed by a solution of 2 per cent, pyrogallic 

 and i per cent, tannic acid. He prefers embedding in 

 celloidin, and uses LoefBer's methylene blue as a counter- 

 stain. 



INDIAN INK METHOD. 



A special method of identifying these and other 

 organisms on a field rendered opaque by means of 

 indian ink has been devised by Burri. For this purpose 

 ordinary indian ink is diluted with water (i part in 6 

 or i in 10). The solution is sterilised and allowed to 

 stand for two weeks, the supernatant fluid being then 

 ready for use. A loopful of suspension of the organ- 

 isms is mixed with a drop of the ink-solution, spread on 

 a slide and allowed to dry. The spirochaetes are then 

 easily seen as colourless spirals on a dark background. 

 Some writers prefer a stronger solution of the ink than 

 that given above, e.g., i in 2 of water. 



EXAMINATION OF LIVING SPIROCHAETES. 



Dark Field Examination. The identification of 

 living spirochaetes of the small varieties is most easily 

 effected by examination on a "dark field" under 

 the microscope, by means of one of the forms of par- 



