_Müller’s Fluid._--Bichromate of potash 30 grains, sulphate of soda 15 grains, distilled water 3-1/2 ounces. This hardens in from three to six weeks. Then transfer, as before, to methylated spirits, and change it every day until colour ceases to appear. Most suitable for lymphatic glands, eye-ball and its internal structures, as well as for tendons, and thymus gland.
_Methylated Spirit_ may be generally employed, but it has a tendency to shrink some tissues too much; it hardens in about ten days. It is usual to change the spirit daily, for the first three days at least. Skin, mammary gland, supra-renal glands, tonsils, and all injected organs may be hardened in it. (See note on the adulteration of methylated spirit with rack-oil, which utterly spoils it for use.)
_Decalcifying solution_ for bones and teeth. Take one-sixth per cent. watery solution of chromic acid, and to every measured ounce add five drops of nitric acid. This reagent will soften the femur of any small animal in about three weeks; larger require a longer time. Change the fluid several times, and test its action by running a needle through the thickest part of the bone. Should it not pass through easily, then continue the process until it does. When soft enough transfer to water, let it soak for an hour or two, then pour off the water and add ten per cent. solution of carbonate of soda, and soak for twelve hours to remove all trace of acid. Wash again in water, and transfer to methylated spirit until required. Teeth require a large quantity of the decalcifying solution for softening.
_Microtomes._--The simplest form of “hand-cutting machine” is that worked by a screw, which raises the preparation, and at the same time regulates the fineness of the section. When a number of sections are required, or when a complete series of sections of an organ is desired, Cole’s simple microtome (Fig. 233) is in every way adapted.
[Illustration: Fig. 232.--Hand Section Cutter.]
[Illustration: Fig. 233.--Cole’s Section Cutting Microtome.]
_The method of using it_ is as follows:--Screw the microtome firmly to the table, and with the brass tube supplied with the microtome, punch out a cylinder of carrot to fit into the well. Cut this in half longitudinally, and scrape out enough space in one half of the carrot to take the specimen; then place the other half of carrot in position, and make sure that the specimen is held firmly between them, but it must not be crushed. Now put the cylinder of carrot and specimen into the well of the microtome and commence cutting the section. A good razor will do, but it is better to use the knife which Messrs. Watson supply with the microtome. While cutting keep the knife and plate of the microtome well wetted with dilute methylated spirit, and as sections are cut place them in a saucer of dilute spirit. A number of sections may be cut and preserved in methylated spirit until required for examination or mounting.