{174} The stain is more conveniently applied upon cover-glasses than upon slides. Films much more than a month old do not stain well. In some localities ordinary tap-water will answer both for diluting the stain and for washing the film; in others, distilled water must be used. Different lots of Wright's fluid vary, and a few preliminary stains should be made with each lot to learn its peculiarities. The principal variation is in the amount of water which must be added to obtain the iridescent scum. Sometimes eight or more drops must be added after the scum appears. When properly applied, Wright's stain gives the following picture (Plate VI): erythrocytes, yellow or pink; nuclei, various shades of bluish-purple; neutrophilic granules, reddish-lilac; eosinophilic granules, bright red; basophilic granules of leukocytes and degenerated red corpuscles, very dark bluish-purple; blood-plaques, dark lilac; bacteria, blue. The cytoplasm of lymphocytes is generally robin's-egg blue; that of the large mononuclears may have a faint bluish tinge. Malarial parasites stain characteristically: the cytoplasm, sky-blue; the chromatin, reddish-purple. _Jenner's stain_, which gives a somewhat similar picture, is preferred by many for differential counting of leukocytes. It brings out neutrophilic granules rather more clearly, but does not compare with Wright's fluid as a stain for the malarial parasite. Unfixed films are stained about three minutes, rinsed quickly, dried, and mounted. For the physician who wishes to use only one blood-stain, Wright's fluid is undoubtedly the best of those mentioned. [Illustration: PLATE VI. EXPLANATION OF PLATE VI. Stained with Wright's stain. All drawn to same scale.