30 W. H. E M I G 



low-brown that gradually disappears when the algae are trans- 

 ferred to glycerin. 



44. Para Red, Azophor Red PN is a developed dye which is 

 not adaptable to paraffin sections. It may be produced on whole 

 mounts by first using an alkaline beta-naphthol solution and then 

 following with an ice cold diazotized paranitroaniline. The 

 orange-red pigment lacks sufficient density for whole mounts. Be- 

 cause Azophor Red is insoluble in water or alcohol, it cannot be 

 used as a stain. 



57. Pontacyl Carmine 6B (Du Pont) is an acid dye, light 3. 

 Thin sections of tissue are fuchsia with a decided bluish cast. A 

 potassium dichromate mordant darkens the color considerably. 

 Numerous tints and shades which are valued in commercial dyeing 

 are not so important in microtechnique where the bright primary 

 colors are preferred. 



73. Sudan II may be used as a fat stain; 1/10 gram in 50 ml. 

 of 95 per cent alcohol and 50 ml. of 1 per cent sulfuric acid. 

 Freehand sections of fresh tissue containing fat become orange- 

 red at 50° C. although starches and proteins remain unchanged. 



74. Scarlet R is an acid dye, insoluble in water. Because it is 

 soluble only in alkaline 50 per cent alcohol, the dye is unsuited for 

 staining paraffin sections. 



79. Ponceau R, 2R, Scarlet R, 2R is an acid dye, light 4. 

 Plant tissues are stained a bright red that contrast well with green 

 basic dyes. It is similar to Ponceau 3R which is more fast. Ani- 

 mal tissues are stained in the same manner as described in the 

 technique for Ponceau 3R, C. I. No. 80. 



80. Ponceau 3R is an acid dye, light 3 ; J gram in 100 ml. of 

 distilled water and 1 ml. of 1 per cent sulfuric acid. On sections 

 of animal tissues use a mixture of three parts Sun Yellow, C. I. No. 

 620, and one part Ponceau 3R for five minutes ; follow with ( 1 ) 

 Niagara Sky Blue, C. I. No. 520, for two minutes or (2) with 

 Aniline Blue, C. I. No. 707, one minute. The results are not 

 satisfactory on a tissue that has been fixed in either picric acid or a 

 chromium salt. 



