Many materials are employed. The most suitable are:--(1) Canada balsam, which is almost colourless and transparent and looks very neat. (2) Gold size. (3) Marine glue. When these are dry a finished appearance may be given to the slide by laying on a ring of zinc white. This is made as follows:-- Oxide of zinc 1/2 drachm. Benzole } half an ounce Gum dammar } of each. *Preservation of sections.*--They should be kept _flat_, and preserved from both light and dust. Very useful cardboard trays are now sold by almost all dealers in boxes made to contain twenty-four dozen slides for about eight shillings, or suitable cabinets may be constructed by a carpenter. CHAPTER V. GENERAL STAINING METHODS. Much information may be obtained from unstained sections, and in most cases one section should be examined unstained, but the specimens mounted in this way are so transparent that it is difficult to study the details of the tissue. They are therefore usually prepared by treating them with some staining reagent, not merely to render them less transparent, but also to “differentiate” the elements of the section, by staining one part more deeply than another, or of a different colour. Thus hæmatoxyline stains the nuclei and rapidly growing parts of the tissue, leaving the formed material, as a rule, much more lightly tinted. Methyl violet again stains healthy tissues blue, and parts affected with waxy degeneration a red-violet colour. By combining stains also much differentiation of the tissue elements may be obtained. Sections should be stained with several reagents, as their effect on individual specimens varies a good deal. The following are the most useful stains for general purposes:-- *Logwood.*--This or its purified principle hæmatoxyline is the most useful general stain. The hæmatoxyline itself is preferable, giving more constant results, and less diffuse staining. For general staining purposes the following formula will be found to give excellent results:--*Hæmatoxyline. Schuchardt’s formula.*-- (_a_) Hæmatoxyline 3 grms. 30 grs. Absolute alcohol 16 c.c. 2-1/2 drms. (_b_) Pure alum 3 grms. 30 grs. Distilled water 100 c.c. 2 ozs. Add (_a_) to (_b_) _drop by drop and with constant agitation_. Keep for some days exposed to diffuse daylight until its colour is so deep that it will not transmit the light. It should then be filtered, and a crystal of thymol added. It will not give very satisfactory staining reactions at first, and should be allowed to ripen at least a month or six weeks before using. It improves as a dye with every month that it is kept. Whenever hæmatoxyline has been made up with alum as in the above formula, an abundant reddish-brown precipitate forms after some time. This in no way interferes with the activity of the solution, but it must always be filtered before being used.