MOUNTING SECTIONS OF HARDENED TISSUE IN CANADA BALSAM OR DAMMAR. Canada balsam, chloroform and turpentine mounting fluid is prepared by mixing: Canada balsam, 105 parts, or 3 ozs. Chloroform, 35 parts, or I oz. When it gets thick add a little chloroform. Canada balsam and xylol.-Dissolve Canada balsam in xylol until it is about the same consistency as the foregoing solution. It dries more slowly and will keep longer without getting thick. Canada balsam and benzole.-To make this solution the Canada balsam must be dried slowly until it becomes quite brittle, it is then dissolved in benzole. The consistency should be about the same as the solution in chloroform and turpentine. It soon becomes thicker, when more benzole must be added. Dammar varnish is prepared thus: Take of Gum Dammar in powder, 1 oz., and dissolve it in turpentine, 1 oz. Filter. Gum mastic, oz., and dissolve it in chloroform, 2 OZ. Filter. Mix the two solutions and filter again. Put in stoppered bottles, and see that they are perfectly free from moisture before using. A small dropbottle of these fluids must be kept for daily use. These mounting fluids are all used in the same manner, and one description will apply equally well to each. The Canada balsam solutions are more commonly used, as the materials of which they are composed are very cheap, while Dammar varnish is more expensive. The Dammar varnish is also sometimes apt to become cloudy after a time, and it is difficult to make. Canada balsam, chloroform and turpentine acts very well with hardened sections, while Canada balsam and xylol is better for stained micro-organisms. TO MOUNT IN CANADA BALSAM OR DAMMAR VARNISH. The sections having been properly stained and washed, are placed in methylated spirit to remove some of the water, and then immediately transferred to a small quantity of absolute alcohol in a watchglass, and covered with another to prevent evaporation. They should be left in this for about 10 minutes. The absolute alcohol, which should be the strongest, sp. gr. 795, has a great affinity for water, and will remove all that is in the sections. When ready remove the sections one by one from the absolute alcohol with a needle, and drain off as much alcohol as possible by touching the section on the back of the hand or on a piece of clean filter paper; the back of the hand is the best, as some fibres from the filter paper may adhere to the section, which when seen under the microscope, will not im prove the beauty of the preparation; when sufficiently drained, without being allowed to become absolutely dry, they are placed in a vessel containing oil of cloves; they will spread out on the surface of the oil, and as the spirit evaporates they will become completely permeated with it and very transparent. If there are any folds these should now be straightened out carefully with needles. Having placed a drop of Canada balsam solution on the slide, spread it out slightly with a needle, select a section in the oil of cloves, and pass the copper lifter under it, raise the lifter and hold the section in position with a needle by its upper corner, and having made sure there are no folds, remove the lifter with the section on it from the oil of cloves, let as much oil drain off as possible against the side of the vessel, and remove the rest by placing the edge of the lifter on a piece of filter paper. Place the edge of the lifter on the slide in the drop of Canada balsam solution, and gently draw down the section with a needle, as soon as a corner projects from the lifter on to the slide, hold it there lightly with the needle and slowly draw away the lifter; if this is carefully done the section will lie in its place in the middle of the slide without any folds. A lifter is made by beating out the end of a copper wire, filing it smooth, and then turning up the broad portion slightly. Take up a cover glass with the broad pointed forceps and hold it between the thumb and fore-finger of the left hand, place a small drop of Canada balsam solution on its lower edge, transfer to the right hand and gently lower it on to the section, keeping the left thumb against one corner to prevent its slipping, and gradually lower it with the forefinger of the right hand very slowly, watching all the time to see that no air bubble is entangled in the section. With a little practice this can be done very neatly without an air bubble in any part of the preparation; it requires patience, however, and it is no use to try air pumps or any dodges, to remove the bubbles, as they are useless; the only thing to be done when an air bubble lodges in a cavity of the section and refuses to move in any way by gentle pressure is to lift the cover glass, and transfer the section to oil of cloves, and then remount it. When several sections are to be mounted on one slide, a slight pressure on each with the needle will generally retain it in its position, if too much of the mounting fluid is not used. It will often be found on examining preparations after they have been mounted some little time, that the fluid has evaporated and left a vacuum under the cover glass; in this case a drop of the mounting fluid must be placed on the slide in contact with the cover glass, and it will immediately run in and fill up the empty space, provided always an egress has been allowed to remain for the contained air; when this is impossible from the small size of the hole at the edge of the cover glass, the only thing to be done is to wait until some of the material, of which the mounting fluid is composed, has been dissolved by the fresh fluid. Applying heat will effect it, and at the same time in all probability ruin the specimen. Each preparation should be examined under the microscope and if found to be worth keeping, labelled. On the label should be noted the tissue, date of its preparation, mode of hardening and staining, thickness of cover glass if it has been measured, and anything of note which may be seen at the time it is examined. Exceptionally good sections should always have a private mark to show that they are not to be given away or exchanged. They should be kept in a cabinet where they may lie flat. ON BREAKING DOWN OLD PREPARATIONS. It is often necessary to break down an old preparation and remount it. The cover glass may be broken, the staining faded, or the cover glass may be too thick, and preparations should never be discarded for these reasons, as it is quite easy to remount them. When a specimen has been mounted in glycerine, it is an easy matter to remove the cover glass, all that is necessary being to cut round the cement with a sharp knife, lift the cover glass carefully with a needle, and float off the section in water; if it is very delicate the cover glass had better be removed under water. The section can then be washed, to remove the glycerine, and re-stained if required; it will then be ready for mounting in the usual manner. To break down a specimen mounted in Canada balsam solution or Dammar varnish is more difficult, especially if it has been mounted long enough to |