METHODS OF OBSERVING BACTERIA. 161 



staining, as it seems to improve with age. The use of 

 acid and alkaline solutions added to the mordant is dis- 

 pensed with. 



The bacteria are carefully fixed to the glass, stained 

 with the mordant for five minutes, warming a little to- 

 ward the end, washed, dried, and subsequently colored 

 with carbol-fuchsin warmed a little. 



Van Ermengem ' has devised a somewhat complicated 

 method of staining flagella which has given great satis- 

 faction to many who have used it. Three solutions, 

 which he describes as the Bain fixateitr, Bain sensibili- 

 sateur, and Bain redncteur et reinforcateur, are to be 

 used as follows : 



i. Bain Jixateur : 



2 per cent, solution of osmic acid, i part ; 



10-25 P er cent, solution of tannin, 2 parts. 



The cover-glasses, which are very thinly spread, dried, 

 and fixed, are placed in this bath for one hour at the 

 room temperature, warmed until steam arises, and then 

 kept hot for five minutes. They are next washed with 

 distilled water, next with absolute alcohol, then again 

 with distilled water. All three washings must be very 

 thorough. 



2. Bain sensibilisateur : 



5 per cent, solution of nitrate of silver in distilled water. 



The films are allowed to remain in this for a few 

 seconds, and are then immediately transferred to the 

 third bath. 



3. Bain reducteur et reinforqateur : 



1 Travaux du Lab. d'hygiene et des bad. de Gand., t. i., p. 3. Abstracted 

 in the Centralbl. f. Bakt. u. Parasitenk., 1894, Bd. xv., p. 969. 

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