STAIN TECHNIQUE 39 



plant host should be tried with alum Haematoxylin and Direct Fast 

 Scarlet 4BS. This latter combination of stains provides the con- 

 trast which has been attempted so often with Haematoxylin and 

 Congo Red. Should Direct Fast Scarlet 4BS be the first stain 

 used on mature plant tissues counterstain the material with Methyl 

 Violet, C. I. No. 680. 



331. Bismarck Brown G, Y, and 332. Bismarck Brown R, 

 Vesuvine R are basic dyes, light 3; J gram in 95 ml. of distilled 

 water, 5 ml. of 5 per cent ammonium alum, and \ ml. of acetic acid. 

 An overnight stain on plant tissues gives an intense brown ; the R 

 shade is the darker. On paraffin sections, Bismarck Brown is not 

 equal to Acridine Orange in fastness. 



353. Pontamine Fast Pink BL (Du Pont) is a direct dye, 

 light 3 to 4. A fuchsia pigment is obtained on paraffin sections of 

 various plant tissues with an acid solution of the dye. With a 

 potassium dichromate mordant, parenchyma is stained brick red. 

 In alkaline solutions of the dye, blue-green algae are colored a fugi- 

 tive pink. 



364. Brilliant Yellow is an acid dye, light 3. For most sec- 

 tions of materials embedded in paraffin the color is too light ; resin- 

 ous tissues stain bright yellow from an acid solution. Blue-green 

 algae are a clear yellow in alkaline solutions. 



365. Chrysophenine is a direct dye, light 4 to 5. This dye is 

 used as a substantive yellow on fabrics for bronze shades. On 

 paraffin sections the stain is too light and too fugitive. 



370. Congo Red is a direct dye, light 4 ; ^ gram in 95 ml. of 

 distilled water and 5 ml. of 5 per cent sodium sulfate. On sections 

 of animal tissues Congo Red is used as a contrast stain with 

 Haematoxylin. The color is not uniformly distributed on most 

 objects because the stain does not have a specific selection for any 

 particular tissue. 



If Congo Red were more fast to light it would be very useful 

 for staining fungous mycelia within a plant host. With materials 

 fixed in Gilson's solution the host appears purple in alum Haema- 

 toxylin; after the section is rinsed in distilled water, the fungous 

 parasite is stained in Congo Red for 24 hours. The dye is so 



