| Saturated alcoholic solution of methylene blue | 3 | volumes. |
| Caustic potash, aqueous solution 1 : 10,000 | 10 | volumes. |
Filter.
This solution is perhaps the most generally useful stain. It colours most bacilli and micrococci, and while rapid in its action rarely overstains. It must be made up fresh on each occasion. It is the best counterstain after staining tubercle bacilli, &c., with fuchsine.
Ziehl’s carbol-fuchsine.
| Carbolic acid (5 per cent. aqueous solution) | 100 | volumes. |
| Fuchsine (saturated alcoholic solution) | 11 | volumes. |
The solution must be filtered immediately before being used.
Gram’s iodine solution.—Sections are placed in this solution after being stained with aniline dyes. The iodine in some way fixes the dye in the organisms, so that they are not decolourised along with the rest of the tissues.
It is made thus:—
| Iodine | 1 | grm. | 1 1/2 | grains. |
| Iodide of potassium | 2 | grms. | 3 | grains. |
| Distilled water | 300 | c.c. | 1 | ounce. |
Ten per cent. aqueous solutions of nitric and sulphuric acids should be prepared and may be kept indefinitely.