42 W. H. E M I G 



on either animal or plant tissues using the combinations of stains 

 given under Niagara Sky Blue, C. I. No. 520. 



520. Niagara Sky Blue, Direct Sky Blue is a direct dye, light 

 3 ; J gram in 95 ml. of distilled water, 5 ml. of 5 per cent sodium 

 sulfate, and J ml. of acetic acid. Niagara Blue 4B is a commercial 

 trade name originating from a former manufacturer of dyes. 

 Frequently it is necessary to employ a dye possessing basic prop- 

 erties, the - NH 2 radical, in order to produce a contrast with acid 

 dyes. Niagara Sky Blue supplies this need in many sections of 

 animal or fungous tissues where the structures are differentiated 

 more clearly than with Aniline Blue, C. I. No. 707. Suggestions 

 for the application of this blue counterstain are given under Sun 

 Yellow, C. I. No. 620, Orange II, C. I. No. 151, Crocein Scarlet 

 MOO, C. I. No. 252, Biebrich Scarlet, C. I. No. 280, and Acid 

 Fuchsine, C. I. No. 692. 



On red and green algae, the polychromatic properties are evi- 

 dent; the spores are tinted red and the vegetative cells, blue to 

 violet. On mature plant tissues, the basic dyes such as Rhodamine 

 6G, C. I. No. 752, Acridine Red, C. I. No. 740, or Safranine, C. I. 

 No. 841, are followed by Niagara Sky Blue for one to five minutes. 

 Should the section consist largely of parenchyma, Biebrich Scarlet 

 and Niagara Sky Blue often supply a vivid contrast. On either 

 fungous tissues or meristems, the orange and red acid dyes such 

 as Orange II, Biebrich Scarlet, or Acid Fuchsine used for 30 min- 

 utes to 24 hours may be followed by Niagara Sky Blue one to five 

 minutes in the same manner as these combinations are used on ani- 

 mal materials. 



Class V. Trisazo Colouring Matters 



581. Erie Black GXOO, Chlorazol Black E, Direct Black E 

 is a direct dye. In the commercial dyeing of cotton, Erie Black is 

 applied at boiling temperature with the aid of a chromium salt. In 

 sections of embryos taken from a fixative containing chromium as 

 in chrom-acetic or Zenker's solution, the dye colors the nuclei black 

 and cytoplasm gray. The dye cannot be used as a general stain on 

 either animal or plant tissues. Parts of a pine needle section are 

 pale blue, dingy green, or dim yellow; on invertebrate and verte- 



