It should be kept in a stoppered bottle with a glass rod fused into the stopper.
When sections are to be stained they are to be floated out on a clean glass slide as described on page [55]. The slide should then be tilted to allow the water to drain off, and superfluous moisture round the section removed by a soft rag, or blotting paper. A drop or two of the stain should then be transferred to the slide, which should be left lying quite flat for about ten minutes. Unless the room is very warm it is advisable to heat the slide very gently over a spirit lamp, as this causes the tissues to stain more brightly and more rapidly.
The excess of the picrocarmine should be allowed to run off the slide, and the latter wiped. Some of the stain should, however, be left on the section, as its effects go on increasing, and are often not fully seen until a few weeks have elapsed. They should be mounted in Farrant’s medium. As a rule those mounted in Canada balsam do not give such good results. Should there be special reasons for using this medium, as in mounting spinal cord sections, &c., they should be dehydrated after staining in picrocarmine in an alcoholic solution of picric acid (one part of a saturated alcoholic solution to five of alcohol), before clarifying in oil of cloves, as otherwise the alcohol will dissolve out the picric acid, and much of the differential staining effect will be lost. The nuclei should be stained a bright crimson, the protoplasm of the cells yellow, or a dull pink, the fibrous elements a bright pink, red corpuscles green, and all dead material, e.g., caseous matter, bright yellow. It also stains nerve-cells, and the axis cylinders of nerve fibres very brightly. It is, however, a rather uncertain dye. The results are most brilliant in the case of fresh sections.
Osmic acid is invaluable for staining fatty particles in the cells.
For ordinary use the one per cent. stock solution (p. [21]) should be diluted with ten times its bulk of distilled water, and sections stained in it all night in a dark cupboard, or the watch glass containing them may be placed inside a small box.
The sections must be washed thoroughly in plenty of water. If desired they may be stained subsequently in picrocarmine or methyl violet if waxy degeneration also be present. Sections should be mounted in Farrant’s solution, as Canada balsam usually gives disappointing results.
It demonstrates the most minute fatty particles in degenerating cells, &c., staining them black. It may be employed to demonstrate the globules of fat blocking up the vessels in fat embolism.
It stains the myelin sheaths of nerves black, and will be again referred to when speaking of methods of staining the spinal cord.
Nitrate of silver is employed for staining the intercellular cement of epithelial cells. It stains this substance a deep black, while the rest of the tissue takes on a brown colour. It is used as a half per cent. solution in distilled water, and kept in a stoppered bottle carefully covered up with brown paper. To use it take some epithelial tissue, e.g., the omentum from a recently killed animal, or a section of some epithelial tumour, immediately after excision. Wash thoroughly in distilled water to remove all chlorides, and then place in a watch glass containing the silver solution. Keep this in the dark for half an hour and then wash thoroughly in plenty of water. The section should be mounted in glycerine or Farrant’s medium and kept from the light or it will become too darkly stained.