use throughout the year if the laboratory is kept fairly warm in winter. Many workers, however, prefer one paraffin melting at 45° C. for winter, and another melting at 48° C. for

summer.

A preliminary bath of soft paraffin is wholly unnecessary, and only prolongs the objectionable stage of heating. The regulator should register only one or two degrees above the melting-point of the paraffin.

Paraffin should be melted and decanted or filtered before use, as it often contains foreign material. When hot it runs

through an ordinary filter without trouble. A hot-water jacket to the funnel is not at all necessary.

Vulcanized Fiber.-For mounting celloidin preparations nothing is so poor as cork, although it has been in use. for years. The chief objections to it are that it does not furnish a rigid support to the imbedded object; that, unless weighted, it floats in alcohol with the specimen downward; and that it yields a coloring material which stains both the

alcohol and the specimen. Wood is not much better, although, of course, much firmer. Glass blocks have been proposed, and might do fairly well if there did not exist an ideal substance-viz. vulcanized fiber. in boards or strips, preferably or sawn to any desired dimensions.

This can be obtained inch in thickness and It is perfectly rigid, is

heavy enough to sink specimens to the bottom of the jar in an upright position, is unaffected by alcohol or water, except that the surface swells and softens very slightly, is light red in color, so that it is easily written on with a lead pencil, gives off no coloring material, and is practically indestructible.

Two or three parallel cuts, I to 2 mm. in depth, should

FIG. 83.--Diagram of the direction of the movements in honing.

be sawn into the upper surface of each block, so as to give the celloidin a firm hold.

Knives.-The knives for both the celloidin and the paraffin microtomes should be heavy and not too long, so as to afford as great rigidity as possible; they should be biconcave, so that they may be easily sharpened. It is important that every one who does much work in a pathological labor

atory should learn to sharpen his own knives. The requisite skill is not difficult to acquire, and the time spent in learning is fully compensated for by the ability always to have a sharp knife when it is wanted. For honing a knife either a fine water-stone or a glass plate with diamantine and Vienna chalk may be used. In honing, the edge of the knife is forward and the motion is from heel to toe. The knife should always be turned on its back, and the pressure on it should be at all times rather light.

In stropping, the movement is reversed. The back of the knife necessarily precedes the edge, and the motion is from

FIG. 84.-Diagram of the direction of the movements in stropping.

toe to heel. The direction of the movements in honing and stropping is best illustrated by the diagrams (Figs. 83, 84).

Running water for washing out specimens which have been fixed in Flemming and other solutions is most easily supplied by having a water-pipe, furnished with numerous cocks 5-10 cm. apart, run horizontally over a slightly sloping shelf adjoining the sink. Attached to each cock is at rubber tube, with a glass tube in the end of it long enough to reach to the bottom of the jar (Fig. 85). By this arrangement the amount of water supplied to each specimen can be easily regulated.

Slides should be of colorless glass with ground edges. The English form, measuring I X 3 inches (76 × 26 mm.), is

to be preferred for ordinary use. Occasionally broader slides are needed.

Cover-slips should be square or oblong according to the shape of the specimen. Most dry lenses are adjusted for cover-glasses measuring 16 or 17 in thickness, so that if possible no cover-slips ranging outside of 15 to 18μ should be used. With an oil-immersion the exact thickness is not quite so important.

Slides and cover-slips are cleaned by dipping in alcohol

and wiping dry with a soft crash towel or old linen handkerchief.

To clean old slides place them in waste alcohol until the cover-slips can be easily removed. The slides and coverslips are then treated separately with nitric acid. A 10 per cent. solution is usually sufficient, but occasionally the strong acid will be found necessary. A thorough washing in running water, followed by alcohol, completes the process. Alkalies are not so good for cleaning purposes, because they attack the glass.

Staining Dishes.-Watch-glasses are not satisfactory,

on account of their instability. Concave dishes with flat bottoms are much better for ordinary use, and can be obtained of several patterns. They should be large enough to hold 25 c.c. of fluid. The Syracuse solid watch-glasses are very good dishes of this shape.

Stender dishes (Fig. 86) of various sizes will be found useful for many purposes.

Oblong rectangular Petri dishes are very convenient for staining preparations mounted on the slide.

Steinach's sieve-dish is valuable where a number of sections are to be stained in the same manner.

Large concave dishes holding 100 c.c. will be found the most convenient for holding frozen sections of fresh tissue, because a slide can be dipped into them and under the sections.

Metal Instruments.-Spatulas of different sizes are

FIG. 87.-Spatula.

needed. They should be thin, smooth, and large enough, so that a section will not curl over the edge (Fig. 87). The best instrument for transfering sections under all cir