Chapter VII 

 BIOLOGICAL STAINS 



B. Natural Organic Dyestuffs 



Since prehistoric times numerous natural dyes have been used in 

 the dyeing of fabrics. It was not until the discovery of the art of 

 mordanting, however, that any considerable advance in dyeing be- 

 came possible. The mordants at first employed consisted of the 

 naturally occuring sulfates of iron and aluminum. 



1239. Carmine, Carminic Acid, or Cochineal is an acid mor- 

 dant dye, light 3 to 4. Cochineal is extracted with water contain- 

 ing ammonium alum from the tropical insect, Coccus cacti, reared 

 on cactus plants in Mexico. The purified red pigment is known 

 as Carmine. The active coloring principle of this dye is Carminic 

 Acid, which, upon the addition of ammonium alum, potash alum, 

 borax, sodium stannate, or sulfuric acid becomes soluble in water. 



The stain is prepared either from the dry powdered cochineal 

 bugs or from the purified Carminic Acid. 



1 . A saturated stain contains 0. 1 gram of Carminic Acid or the 

 extract from 0.5 gram of powdered bugs in 100 ml. of 0.2 per cent 

 sulfuric acid at 50° C. ; several hours is necessary to effect complete 

 solution. Filter the hot liquid and add 20 per cent alcohol by vol- 

 ume. Invertebrates or chick embryos are placed in a tin mordant 

 for 30 minutes ; they are stained a brilliant scarlet within 30 min- 

 utes at 50° C. This solution is unsatisfactory for paraffin sections 

 unless the material is first stained in bulk. 



2. Dissolve 0.1 gram of Carminic Acid or extract 0.5 gram of 

 cochineal bugs in 100 ml. of 1 per cent ammonium acetate in 20 per 

 cent alcohol. A brilliant carmine is obtained on whole mounts of 

 invertebrates with a 30-minute mordant in 5 per cent ammonium 

 alum and a stain for 30 minutes at 50° C. This ammonium acetate 

 solution may be used for paraffin sections although the red devel- 

 oped in 24 hours is not so good as the color obtained by staining in 

 bulk. 



3. Carmine dissolves in a solution of 5 per cent ammonium alum 



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