While it is true that some bacteria may be stained by that standard histological nuclear dye, hematoxylin, it is of little value for this purpose. Practically all bacteriological stains are solutions of the anilin dyes. These dyes, as is well known, are of nearly every conceivable color and shade but relatively very few are used in bacteriological work. The beginning student will rarely use solutions of other than the three dyes fuchsin (red), methylene blue and gentian violet for staining bacteria, with occasionally Bismarck brown, or eosin, or safranin as tissue contrast stains.
The bacteriological dyes are kept “in stock” as saturated solutions in 95 per cent. alcohol which are never used as stains, but merely for convenience in making the various staining solutions.
The approximate percentages of the three common dyes in such solutions are indicated in the following table adapted from Woods Chemical and Microscopical Diagnosis, Third Edition, 1917, Appendix:
| Fuchsin | 3.0% |
| Gentian Violet | 4.8% |
| Methylene Blue | 2.0% |
The stains made from these dyes which are in most common use are the following:
| Saturated alcoholic solution of gentian violet | 1 part |
| Distilled water | 20 parts |
| Mix well and filter. | |
| Saturated alcoholic solution of gentian violet | 1 part |
| Anilin water (see [below]) | 10 parts |
| Mix well and filter. | |
| Saturated alcoholic solution of fuchsin | 1 part |
| Anilin water (see [below]) | 10 parts |
| Mix and filter. | |
These stains rarely keep longer than ten days in the laboratory (unless kept in the ice-box) and must be made fresh on the first sign of a deposit on the glass of the container.
Anilin Water.—Anilin water is made by putting 3 or 4 cc of anilin “oil” in a 120 cc. flask, adding 100 cc of distilled water, shaking vigorously for a minute or so and filtering through a wet filter, in other words, a saturated solution of anilin in water.