For the ordinary staining reagents (in watery fluids) it is enough to place the air-dried preparation at about 110 deg. C. for one half to two minutes. For differential staining mixtures, for instance the eosin-aurantia-nigrosin mixture, a time of two hours is necessary, or higher temperatures must be employed. 2. Chemical means. _a._ To obtain a good triacid stain, the preparations may be hardened, according to Nikiforoff, in a mixture of absolute alcohol and ether of equal parts, for two hours. The beauty of specimens fixed by heat is however not quite fully reached by this method. _b._ Absolute alcohol fixes dried specimens in five minutes sufficiently to stain them subsequently with Chenzinsky's fluid, or haematoxylin-eosin solution. It is an advantage in many cases, especially when rapid investigation is required, to boil the dried preparation in a test-tube in absolute alcohol for one minute. _c._ Formalin in 1% alcoholic solution was first used by Benario for fixing blood preparations. The fixation is complete in one minute, and the granulations can be demonstrated. Benario recommends this method of fixing, especially for the haematoxylin-eosin staining. These methods are described as the most suitable for blood-investigation in general. For special purposes, for instance, the demonstration of mitoses, blood platelets, etc., other hardening reagents may be used with advantage: Sublimate, osmic acid, Flemming's fluid, and so forth. [gamma]. Staining of the dry specimen. Staining methods may be classified according to the purpose to which they are adapted. We use first those which are suitable for a simple general view. For this it is sufficient to use such solutions as stain haemoglobin and nuclei simultaneously. (Haematoxylin-eosin, haematoxylin-orange). Occasionally a stain is desirable which only brings out, but in a characteristic manner, a special kind of cell, _e.g._ the eosinophils, mast cells, or bacteria. Single staining is attained on the principle of maximal decoloration. (Cp. E. Westphal.) Finally, we have panoptic staining; that is, by methods which bring out, as characteristically as possible, the greatest number of elements. Although we must use high magnifications with these stains, we are compensated by a knowledge of the blood condition that cannot be reached in any other way. A double stain is generally insufficient, and at least three different dyes are used. Successive staining was formerly used for this purpose. But everyone who has used this method knows how difficult it is to get constant results, however careful one may be in the concentration and time of action of the stain. Simultaneous staining offers undoubted and important advantages. As there is much obscurity with regard to the principle on which it rests we may here shortly explain the theory of simultaneous staining.