72 .A MANUAL OF BACTERIOLOGY 



may also be stained by other aniline dyes if the 

 solution be made alkaline by the addition of caustic 

 potash or soda.' 



To stain the flagella of certain microbes, Koch 

 recommends that the cover-glass preparations should 

 be floated on a concentrated aqueous solution of 

 hsematoxylin. They are then transferred to Muller's 

 fluid, 1 or to a five per cent, solution of chromic acid. 

 By using either of these reagents the flagella are 

 stained a brownish-black colour. 



On the other hand, Dr. Dallinger 2 does not think 

 that Koch's method of staining brings out the 

 flagella well. Dallinger uses high powers and the 

 microbes alive. 



Dr. Crookshank has, however, succeeded in photo- 

 graphing the flagella by staining with a concentrated 

 alcoholic solution of gentian violet. The prepara- 

 tion is then rinsed in water, dried, and mounted in 

 Canada balsam. 



Gram's method for staining microbes in tissues is 

 as follows : The sections containing the microbes are 

 soaked in absolute alcohol for twelve minutes, and 

 then placed in a gentian-violet-and-aniline solution 3 

 for about three minutes. The sections are then 

 placed in a solution of iodine (in potassium iodide) 

 for several minutes, or until they are of a brown 

 colour. After this they are transferred to absolute 



1 This fluid contains 2 grammes of potassium bichromate, 

 1 gramme of sodium sulphate, and 100 cc. of distilled water. 



2 Journal of Royal Microscopical Society, 1878, p. 172. 



3 This is similar to Koch's methyl-violet-and-aniline stain, 

 except the methyl violet is replaced by gentian violet. 



