14. _Carmine Staining._—In the case of animal sections, carmine is, as a rule, to be selected, giving as it does most satisfactory and beautiful results. Tissues may be stained with carmine by two different plans: in the first, a strong solution is used, and the tissue subjected to its action for a very short period only, whilst in the latter only very weak solutions are employed, the time of immersion being considerably prolonged. The rapid method, however, is not to be recommended, for the strong carmine acts so powerfully upon the tissue as to give the various elements comprising it no time, as it were, to exercise their power of quantitive selection, but involves the whole in one uniform degree of shadeless colour. By adopting the gradual method much better results are obtained, each portion of the tissue being now at liberty to acquire its own particular shade. Amongst the various formulæ for the preparation of carmine fluid, none can be so safely followed as that devised by Dr. Lionel Beale. It runs thus:—Place ten grains of the finest carmine in a test tube, add thirty minims of strong liquor ammonia, boil, add two ounces of distilled water, and filter; then add two ounces of glycerine, and half an ounce of rectified spirit—this solution ought to be kept in a well stoppered bottle. The best vessels in which to stain sections are small jars of white porcelain, capable of holding about two fluid ounces, and furnished with lids—they are much preferable to beakers or watch glasses, for owing to the white background which they afford it is very easy to watch how the staining is proceeding. The carmine solution which we have just described is both too strong and of too great density to be used in its pure state. It will, therefore, require to be diluted with distilled water before use—the most useful degree of dilution being attained by adding one part of stain to seven of water. Sections may be placed in this solution for twenty-four hours, in which time they will usually be found to have acquired a sufficient depth of colour. If, however, the tissue be unusually difficult to stain, the time of immersion may be doubled, or still further prolonged, without detriment to the section. [Illustration: SECTION SPOON.]