Chloride of gold is employed to demonstrate the peripheral terminations of nerves. It can only be employed within the first half hour after the tissue has been removed from the living body. The pieces of tissue must be small and may be stained in bulk, sections being subsequently made.
A half per cent. solution in distilled water is employed. The tissue is transferred to this on its removal from the body, until it becomes lemon coloured. It is then exposed in a one per cent. solution of acetic acid to a strong light until it assumes a purplish tinge, which takes from two hours to two days. Sections should be mounted in Farrant’s medium. It stains the cells of the tissue, and nerve cells reddish purple, and nerve fibrils, especially the terminal ones, rather more violet. This is very well seen in the cornea.
It is useful sometimes for clinical purposes to excise a portion of muscular tissue and examine the nerve endings by this method. Unfortunately the stain is somewhat uncertain in its action. Better results are obtained by Sihler’s chloral hæmatoxyline method (p. [92]).
Methyl violet.—A very satisfactory solution may be obtained ready made in the “telegraphen tinte,” prepared by Leonhardi, of Dresden, as recommended by Woodhead. It may also be used as a one per cent. solution in distilled water, a few drops of carbolic acid being added to prevent the growth of fungi.
It is a very useful selective stain. It gives two reactions, red violet, and blue violet. Thus it stains the matrix of hyaline cartilage blue violet, but the cells red violet. It has also a most important pathological application, as it picks out any parts which have undergone “waxy” or “lardaceous” degeneration, staining them red violet, but the rest of the section blue violet.
About ten drops of a one per cent. solution should be filtered into a watchglassful of water, and the sections stained for about five minutes. They must then be passed through a half per cent. solution of acetic acid and washed thoroughly for some time in a large quantity of water till no more colour comes away.
If these steps are not taken with care, the dye will diffuse out after the section has been mounted, blurring all details and spoiling the appearance of the section.
Sections may be mounted in Farrant’s solution (to which a spot of formic acid may be added): if mounted in Canada balsam the sections must be overstained as both the alcohol and oil of cloves rapidly dissolve out the dye.
Safranine.—Employed as a freshly made saturated solution in aniline oil water warmed to 60° C. (140° F.). Filter into a watch glass. Stain for not more than a minute. Dehydrate in alcohol which will remove much of the stain, clarify in oil of cloves or origanum oil. Mount in balsam.