STAIN TECHNIQUE 41 



448. Benzopurpurin 4B is a direct dye, light 4 to 5. This dye 

 is less intense and more fugitive than Congo Red. It may be used 

 in vital staining. 



450. Benzopurpurin B is a direct dye, light 4. Parenchyma 

 is stained a bright fugitive red. 



463. Azo Blue is a direct dye, light 4. Azo Blue was the first 

 blue azo dye known ; it was seldom used because of the ugly reddish 

 shade produced on fabrics. For paraffin sections the color is too 

 fugitive. It is polychromatic, staining nuclei red and cytoplasm 

 blue. For polychromatic staining with a direct blue dye use 

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



477. Diamine Blue 3B, Trypan Blue is a direct dye, light 4. 

 Parenchyma is stained a bright blue; nuclei are sometimes tinted 

 red. It is used as a vital stain. 



495. Benzopurpurin 10B is a direct dye, light 4 to 5. The 

 bright red on parenchyma is similar to the color produced by Congo 

 Red. 



502. Benzoazurine G is a direct dye, light 4. Sometimes the 

 stain is polychromatic; then, the nuclei of parenchyma retain red; 

 the cytoplasm, blue to blue-violet. In green algae previously 

 treated with copper sulfate, spores are tinted orange-red ; the vege- 

 tative cells are dark blue or violet. 



518. Niagara Sky Blue 6B is a direct dye, light 3; i gram in 

 95 ml. of distilled water, 5 ml. of 5 per cent sodium sulfate, and J 

 ml. of acetic acid. The two best direct blue dyes are Niagara Sky 

 Blue 6B and Niagara Sky Blue, C. I. No. 520. The former dye 

 cannot be used on tissues fixed with Gilson's solution, the latter can. 

 There is little difference in the appearance of the dye powders or 

 the solutions but the results obtained from the two stains are unlike. 

 The first dye is a shade lighter blue, requires two or three times as 

 long for staining, and, in combinations with Sun Yellow, C. I. No. 

 620, gives a clear brilliant green. For a contrast in green and red, 

 with tints of yellow and blue, use a mixture of nine parts Sun Yel- 

 low and one part Acid Fuchsine, on sections of animal or fungous 

 tissue for 10 to 30 minutes, and counterstain in Niagara Sky Blue 

 6B, two or three minutes. Niagara Sky Blue 6B should be tried 



