cells of the villi are blue, the goblet cells reddish; in a hair-follicle the sheath of Henle is an intense red, and the sheath of Huxley blue. 5. Ehrlich-Biondi-Heidenhain Stain, Saturated watery solution of orange acid fuchsin 100 CC. 50 To get complete saturation it is necessary to have an excess of the crystals for several days. Each fluid is saturated separately. Before use, the solution is diluted in the proportion of 1 in 100 with water, and then on the addition of acetic acid must be bright red. It is better to obtain the mixture from Dr Grübler. Application. (1.) Harden the organ in corrosive sublimate. (2.) Stain sections in the dilute solution (12-24 hours). (4.) Dehydrate in absolute alcohol. (5.) Xylol-balsam. It is especially useful for sections containing many leucocytes, and is best used for paraffin sections fixed on a slide. Red bloodcorpuscles are stained red, resting nuclei blue, mitotic figures and nuclei of leucocytes green-violet. General Remarks on Staining.-Filter the staining fluid. When possible, use a weak solution of the dye, and thus let the sections stain slowly in a fairly large amount of the fluid. Place a piece of blotting-paper on the inside of a large watch-glass, pour some of the diluted stain into the watch-glass, and place the sections in it. The sections should lie as flat as possible, and not overlap each other. The sections may be moved gently in the fluid by means of a needle. Cover the watch-glass with another glass of the same size, or set it aside in a moist chamber, e.g., on a plate covered by a bell-jar, with a piece of moistened blotting-paper attached to the inside of the jar (fig. 47). After staining, the sections are to be carefully washed in distilled water to remove any trace of surplus dye (except in the case of picro-carmine). Sections stained with hæmatoxylin should be washed for a long time in water before they are mounted in glycerine or Farrant's solution. Be careful not to over-stain the tissue, except in those cases where the excess can be again removed, e.g., with the aniline dyes by means of alcohol or acid alcohol. All acids should be removed from the sections before they are placed in the dye. It is convenient on many occasions that the student should rapidly stain his sections on a slide, but he should also be taught to practise the slower method of staining sections in very dilute solutions of a dye. There is one method of staining sections which may be profitably impressed upon the student, viz., that so strongly insisted upon by Ranvier. Suppose any delicate object-isolated epithelial or other cells -to be mounted in a watery medium; a drop of a solution of picrocarmine is placed at one side of the cover-glass. As the fluid evaporates at one side of the coverglass the picro-carmine slowly diffuses under the cover-glass and stains the preparation. Exposed to the air, the preparation would soon become dry. This must be corrected. This is best done by placing the slides to be stained FIG. 47.-Support of Ranvier for Holding Slides Placed in this way on a stage under a Bell-Jar. with several shelves (fig. 47), the whole being placed on a plate moistened with a few drops of water and covered by a bell-jar. This forms a moist chamber. After the cells are stained, glycerine may then be applied at the side of the cover-glass, with the same protective precautions, so that the preparation can be finally mounted and preserved in glycerine. XIII.-CLEARING OR CLARIFYING REAGENTS. Glycerine, Farrant's Solution, and Glycerine Jelly.-When any one of these reagents is used for mounting preparations, no other clarifying substance is used. Balsam Preparations. When a preparation is to be mounted. in balsam, be it Canada balsam or dammar, some clarifying reagent has to be added to the preparation before the balsam is applied. Before applying the balsam the tissues must have been rendered transparent. The following substances are most commonly used :-Oil of cloves, a mixture of creosote and turpentine, turpentine, creosote, xylol, cedar-oil, bergamot oil, lavender oil, origanum oil, &c. Oil of Cloves has this advantage, that it clarifies rapidly and does not evaporate, so that sections may be left exposed to the air in it for some time. It renders the sections very hard. It, however, is not so satisfactory for aniline dye specimens, as it is apt to abstract their colour. Moreover, it becomes yellow with age. Creosote is specially useful for preparations which one does not desire to harden in alcohol; do not use metallic instruments. Creosote and Turpentine.—When the fluids are mixed a cloudiness appears, but this disappears on keeping. It is much cheaper than clove-oil, but it rapidly evaporates (one part creosote to four of turpentine). Xylol is perhaps the best, and is specially useful with aniline dyes. In these cases the balsam-Canada or dammar-should also be dissolved in xylol. Cedar-Wood Oil clarifies very slowly. It does not, however, abstract the aniline dyes, and is used for special purposes, as indicated in the context. Origanum Oil is used for clarifying sections embedded in celloidin. Xylol-Aniline Oil.-Equal parts of xylol and aniline are used for clarifying sections under certain conditions without the previous use of alcohol. (Weigert's method, Lesson III.) Carbolic Acid and Xylol.--A mixture of 1 part of carbolic acid and 3 of xylol is used to clarify celloidin sections (p. 47). The section can be taken from 70 per cent. alcohol, and does not require to be further dehydrated. To remove the water from the mixture, keep in the bottom of the bottle containing it a thick layer of previously-heated copper sulphate. General Remarks.-Although several essential oils are used for clarifying purposes, it is not immaterial which one is used. Thus clove-oil may be used for clarifying sections stained with animal or vegetable dyes (carmine), while it is inapplicable for aniline staining, as it dissolves aniline dyes. In many cases the result may be obtained more gradually by using a mixture of half alcohol and half essential oil. Moreover, clove-oil dissolves celloidin, so that it cannot be used when the section fixed on the slide contains either celloidin or collodion. Oil of bergamot does not dissolve celloidin. XIV. MOUNTING FLUIDS, AND METHODS. The fluid chosen will depend on the nature of the tissue and other circumstances. 1. If a section is to be mounted direct from water, glycerine, Farrant's solution, or glycerine jelly may be used. 2. If a section is to be mounted in balsam, it must have every truce of water removed by alcohol, and the alcohol must be displaced by one of the clarifying reagents-xylol, clove-oil, &c.— already mentioned. Glycerine. Pure glycerine is only used for such tissues as have been previously hardened. In the case of tissues-delicate tissues which have not been previously hardened or fixed-the direct application of pure glycerine would injure them. In this case, the best way is to mount the object in normal saline, and at one edge of the cover-glass to place a drop of a mixture of equal parts of glycerine and water. Put the preparation in a plate covered by a bell-jar-an extempore moist chamber. The glycerine slowly penetrates as the water evaporates. Some tissues are rendered too transparent by glycerine, and, moreover, it is very difficult to seal up and keep tight glycerine preparations. Glycerine and Formic Acid. This is sometimes used, especially for picro-carmine preparations. It is made by adding formic acid. to dilute glycerine (1 per cent.). Farrant's Solution. This is for many preparations far more serviceable than glycerine, as it does not render some tissues so transparent as glycerine, and the preparations can be easily sealed up or ringed.' Preparation (Hamilton's receipt).-Make a saturated solution of arsenious acid in water by boiling. After standing for twentyfour hours filter. Take equal quantities of water, glycerine, and arsenious water, and to the mixture add picked gum-arabic. Let the latter dissolve until a thick syrupy fluid is obtained, which takes about a week at an ordinary temperature, but it must be stirred frequently. Filter slowly through filter-paper, which must be frequently changed. Glycerine Jelly.-Melt it in hot water, place a drop on the section, apply a cover-glass, and gently press it down. It gelatinises in a few minutes. Canada Balsam.-Place some Canada balsam in a capsule or wide-mouthed bottle near a fire or in a warm chamber (65° C.) until it becomes hard. Let it cool. This dry balsam is to be dissolved in some medium. Some use chloroform, others benzol, others a mixture of both, or turpentine as a solvent. In any case, |