The eosine-methylene blue mixtures are exceptional in so far, that it is possible with them, for a short time at least, to preserve active solutions, in which with an excess of basic methylene blue, enough eosin is dissolved for both to come into play. A drawback however of such mixtures is, that in them precipitates are very easily produced, which render the preparation quite useless. This danger is particularly great in freshly prepared solutions. In solutions, such as Chenzinsky's, which can be kept active for a longer time, it is less. Hence fresh solutions stain far more intensely and more variously than older ones, and are therefore used in special cases (see page 46). If the stain is successful the appearances are very instructive. Nuclei are blue, haemoglobin red, neutrophil granulation violet, acidophil pure red, mast cell granulation deep blue, forming one of the most beautiful microscopic pictures. For practical purposes, besides the iodine and iodine-eosine solution described below (see page 46) the following are especially used: 1. =Haematoxylin solution with eosin or orange g.= Eosin (cryst.) 0.5 Haematoxylin 2.0 Alcohol abs. Aqu. dest. Glycerine _aa_ 100.0 Glacial acetic acid 10.0 Alum in excess The fluid must stand for some weeks. The preparations, fixed in absolute alcohol, or by short heating, stain in from half-an-hour to two hours. The haemoglobin and eosinophil granules are red, the nuclei stain in the colour of haematoxylin. The solution must be very carefully washed off. 2. In the practical application of the triacid fluid, particular care must be taken, as M. Heidenhain first shewed, that the dyes are =chemically pure=[6]. Formerly granules, apparently basophil, were frequently observed in the white blood corpuscles, particularly in the region of the nucleus. They were not recognised, even by practised observers (_e.g._ Neusser) as artificial, but were regarded as preformed, and were described as perinuclear forms. Since the employment of pure dyes these appearances, whose meaning for a long time puzzled us, are but seldom seen. Saturated watery solutions of the three dyes are first prepared, and cleared by standing for some considerable time. The following mixture is now made: 13-14 c.c. Orange-g. solution 6-7 c.c. Acid fuchsin solution 15 c.c. Aqu. dest. 15 c.c. Alcohol 12.5 c.c. Methyl green 10 c.c. Alcohol 10 c.c. Glycerine These fluids are measured in the above-mentioned order, with the same measuring glass; and from the addition of methyl green onwards the fluid is thoroughly shaken. The solution can be used at once, and keeps indefinitely. The staining of the blood specimen in triacid requires only a little fixation, cp. page 35. The stain is completed in five minutes at most.