a second in which the object is raised by being moved up an inclined plane. The first type of machine is the better, for two reasons: the screw affords greater accuracy in the even elevation of the object than is possible with an inclined

plane, and the object remains at all times in the same relative position with regard to the knife, so that an equally long sweep of the blade can be obtained for every section. An excellent instrument of this type is made by Bausch & Lomb (Fig. 101). For practical work it is much to be preferred to the elaborate Schiefferdecker-Becker microtome, designed for cutting sections under alcohol.

A new and wholly original microtome, in which the knife. remains fixed and is clamped at both ends, while the objectholder, which is raised by a screw, moves back and forth beneath the knife, has recently been designed by Dr. C. S. Minot and is manufactured by Bausch & Lomb (Fig. 102). It is intended both for celloidin and for paraffin work. When but one instrument can be afforded, it is believed that this model will be found the most serviceable for both kinds of work.

A drop-bottle on an elevated stand, with screw arrangement for regulating the amount of alcohol, is the most con

venient method for keeping the object and the knife wet while cutting; 80 per cent. alcohol should be used.

Paraffin Microtome.-Although paraffin sections can be cut on a celloidin microtome, it is preferable to have an instrument designed for the purpose. The Minot wheel microtome manufactured by Bausch & Lomb (Fig. 102 a) can be thoroughly recommended.

Paraffin Bath.-The best bath for keeping paraffin at a constant temperature is a thermostat of suitable size with

hot-water jacket, such as is used for growing cultures of bacteria. The paraffin is kept in it on shelves in glass dishes of various sizes. The advantages of this method over the old way of using copper cups set into the top of a waterbath are that the paraffin is kept absolutely free from dust, each worker can have his own set of dishes, and the smallest bits of tissue can be readily found in them, because they are transparent.

A paraffin melting at 50° to 52° C. will be found convenient for 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. This can be obtained

in boards or strips, preferably or inch in thickness and sawn to any desired dimensions. 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, 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, 1 to 2 mm. in depth, should

FIG. 104. 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

FIG. 105.-Diagram of the direction of the movements in stropping.

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 toe to heel. The direction of the movements in honing and stropping is best illustrated by the diagrams (Figs. 104, 105).

Running water for washing out specimens which have been fixed in Flemming and other solutions is most easily

FIG. 106.-Large laboratory sink, showing adjoining shelf and arrangement for running water.

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 a rubber tube, with a glass tube in the end of it long enough to reach to the bottom of the jar (Fig. 106). By this arrange