COLORING AGENTS. 6l 



contains too much of the coloring matter the mass 

 in which the bacteria lie stains too deeply. After 

 the process of staining is finished, the preparation 

 is rinsed with distilled water, or with a ten per 

 cent, solution of potassic acetate. 



After lying for half an hour exposed to the air, 

 the slide is ready for mounting in balsam. Gly- 

 cerine cannot be used, as it removes the color. 

 Preparations which are to be photographed should 

 be mounted in a fifty per cent, solution of potassic 

 acetate and sealed air-tight. 



The coloring matter is so quickly taken up by 

 the bacteria that we have in it a useful reagent 

 for these organisms, which might be easily con- 

 founded with small oil globules or other very 

 minute rounded bodies. 



ANILINE BLUE. 



Wilhelm t and Russow 2 have recommended an 

 aqueous solution of this dye for staining the cal- 

 lous-plates of sieve-tubes. After the sections have 

 been submitted to the action of the dye they are 

 rinsed in water. The protoplasm colors violet- 

 blue ; the nuclei, deep indigo. Cellulose mem- 

 branes assume a blue color, while the callous- 

 plates become azure. Preparatiens mounted in 

 glycerine change in a few days, so that only the 



1 Wilhelm: Siebrohren, 1880, p. 36. 



8 Russow: Sitzber. A naturf. Ges., Dorpat, 1881, p. 63. 



