1. The hardening process is a slow one occupying four to eight weeks.
2. The fluid gives a permanent dingy colour to the tissue. This does not cause any inconvenience for microscopic purposes, but it is a disadvantage when it is intended to preserve the rest of the specimen, as a naked eye preparation. In such cases the organ should be hardened in spirit, carbolic acid, or formal.
Müller’s fluid can be used for almost any tissue. It is especially useful for those which contain a large quantity of fluid, or of blood, and is essential for nerve tissues which it is intended to stain by Pal’s method (p. [89]).
To harden a specimen in it at least twenty times the bulk of fluid must be employed.
The fluid must be changed on the third day, and afterwards about every week as may be required.
Methylated spirit is a very useful hardening agent. It hardens in one to three weeks according to the size of the tissue and the quantity of spirit used. Its disadvantages are:—
1. It is more apt to overharden than Müller’s fluid.
2. It causes a great deal of shrinking of the tissue and thus squeezes much of the blood out of the vessels.
It is most useful in hardening tissues containing much epithelium, e.g., kidney, epithelioma, &c.