GENERAL REMARKS ON STAINING 73 



The mere selection of two colors which contrast well is not sufficient. 

 Green and red contrast well, but safranin and iodine green would be 

 a poor combination, for both would stain chromosomes and neither 

 would stain the spindle ; both would stain lignified structures and nei- 

 ther would give satisfactory results with cellulose walls. Both stains 

 are basic. Acid green would have given a contrast in both these cases, 

 because it stains achromatic structures and cellulose walls. In general, 

 an acid stain should be combined with a basic one, but there are so 

 many exceptions that it is hardly worth while to learn a list of basic 

 and acid stains. Stains which stain chromosomes are likely to be basic, 

 and those which do not stain chromosomes are likely to be acid or neu- 

 tral. If it were true that acid stains affect only basic structures, and 

 basic stains affect only acid structures, a classification of stains would 

 be of great value. Safranin and gentian violet are both basic but, with 

 the safranin properly washed out and the gentian violet properly ap- 

 plied, chromosomes stain red while the spindle stains violet. Lignified 

 cell walls stain red, while cellulose walls stain violet. The exine of a 

 pollen grain stains red while the intine stains violet. It is very evident 

 that, to secure a contrast, it is not necessary that one stain be basic 

 and the other acid. The only way to insure success is to become 

 famihar with the action of each stain upon the various structures. 



THEORIES OF STAINING 



The history of staining does not go back to Aristotle, but a carmine 

 was used for microscopic purposes as early as 1770. Even in 1838, 

 when Schleiden announced his cell theory, staining had not become an 

 important part of histological technique, although some use was being 

 made of carmine and iodine. Beginning with 1850, stains were used 

 more and more and, during the last thirty years of the century, de- 

 mands for better stains became so insistent that in Germany com- 

 panies were formed to furnish stains for microscopic use. The famous 

 Griibler Company is still furnishing excellent stains, some of which, 

 like their haematoxylin, have not been surpassed. During the World 

 War, stains were produced in America and, when the Commission on 

 Standardization of Biological Stains was organized, stains improved 

 rapidly and many of them have become not only excellent but uni- 

 form, so that, when a stain has become valuable for some particular 

 purpose, one can get more exactly like it. 



