Small pieces should be hardened in this fluid for twelve to twenty-four hours, and then washed and transferred to alcohol for some days before staining.
3. Nitric acid.—A ten per cent. solution in distilled water. It hardens the tissue in three to four hours, and should be followed by 70 per cent. alcohol, the hardening being completed in absolute alcohol.
In using any of these methods it is necessary that the tissue be removed from the body during life or immediately after death. They are employed for revealing the changes in the cells and their nuclei in rapidly growing or inflamed tissue, for studying karyokinesis in cancer cells, and investigating the appearance of nerve cells and gland cells at rest, when actively employed and when fatigued; and they are also most useful in preparing specimens of the “parasitic bodies” which have been described in many cancer cells.
Decalcifying Fluids.
Used in the preparation of bone, tooth, osseous tumours, &c. The two best fluids for general use are:—
Chromic and nitric fluid.—This is made as follows:—
| Chromic acid | 1 | gramme | 45 | grains. |
| Nitric acid | 2 | grammes | 1 1/2 | drachms. |
| Water | 200 | c.c. | 1 | pint. |
If the bone is not very compact the fluid may be used diluted with an equal quantity of water. A large quantity of fluid should be used, and like all decalcifying fluids, it should be frequently changed.
As soon as the specimen is sufficiently flexible, it should be thoroughly washed in running water for some hours, and then transferred to spirit until it is convenient to cut sections.