METHOD OF J)E AOSSI. 179 



cells without tearing the flagella ; allow to dry in air ; 

 fix in gas-flame by holding slip between the fingers (not 

 forceps) and passing through the flame once (not more). 

 They are then to be treated with a mordant made as 

 follows : Dissolve 5 grammes of tannic acid in 20 c.c. 

 of water and filter twice; to 10 c.c. of the filtrate add 

 5 c.c. of a saturated watery solution of cupric sulphate 

 and 1 c.(3. of a saturated alcoholic solution of fuchsin. 

 Filter the mixture twice. Treat the cover-slips with 

 the filtered mordant for two or three minutes at room- 

 temperature. Then wash them thoroughly in water 

 and stain for three or five minutes in the ordinary way 

 (without heating) in the Koch-Ehrlich aniline-water 

 fuchsin solution. Wash in water thoroughly, or for a 

 few seconds in 50 per cent, alcohol and then in water. 



Durham's Method. — Prepare cover-slips according 

 to the methods given above. Place them face down in 

 the following mixture : Saturated solution of stannous 

 chloride (SnCy, 1 part ; 15 per cent, solution of tannin, 

 1 part ; saturated alcoholic solution of methylene-blue, 

 a few drops. Warm for a few minutes, and allow to 

 cool. Wash cover-slip in distilled water. It will be 

 found covered with precipitate, which may readily be 

 removed by washing in warm tannin solution. Care 

 must be taken in doing this, as the tannin solution is 

 apt to deprive the preparation entirely of its color. 

 After removing the precipitate with tannin solution the 

 preparation may be washed in water and restained. 



Method of De Rossi. — Prepare cover-slips as di- 

 rected above from agar-agar culture not over four days 

 old. Mix the bacteria gently through a drop of dis- 

 tilled water placed on the cover-slip, without smearing 

 the drop over the surface. Dry the preparation over 



