1, Normal red corpuscle for comparison; 2, normoblasts, one with lobulated nucleus; 3, megaloblast and microblast. The megaloblast shows a considerable degree of polychromatophilia; 4, blood-plaques, one lying upon a red corpuscle; 5, lymphocytes, large and small; 6, large mononuclear leukocyte; 7, transitional leukocyte; 8, polymorphonuclear neutrophilic leukocytes; 9, eosinophilic leukocytes, one ruptured; 10, basophilic leukocyte; 11, neutrophilic myelocyte. The granules are sometimes less numerous and less distinct than here shown; 12, eosinophilic myelocytes; 13, basophilic myelocyte; 14, "irritation" or "stimulation" form, with small vacuoles; 15, degenerated leukocytes: two polymorphonuclear neutrophiles, one ruptured, one swollen and vacuolated; and a "basket cell" composed of an irregular meshwork of nuclear material; 16, large mononuclear leukocyte containing pigment-granules: from a case tertian malaria; 17, four stages in the asexual cycle of the tertian malarial parasite: the second and fourth were drawn from the same slide taken from a case of double tertian; 18, red corpuscle containing tertian parasite and showing malarial stippling; 19, estivo-autumnal malarial parasites: two small ring forms within the same red cell, and a crescent with remains of the red corpuscle in its concavity.] {175} B. STUDY OF STAINED FILMS Much can be learned from stained blood-films. They furnish the best means of studying the morphology of the blood and blood parasites, and, to the experienced, they give a fair idea of the amount of hemoglobin and the number of red and white corpuscles. A one-twelfth-inch objective is required. 1. Erythrocytes.--Normally, the red corpuscles are acidophilic. The colors which they take with different stains have been described. When not crowded together, they appear as circular, homogeneous discs, of nearly uniform size, averaging 7.5 µ in diameter (Fig. 84). The center of each is somewhat paler than the periphery. The degree of pallor furnishes a rough index to the amount of hemoglobin in the corpuscle. They are apt to be crenated when the film has dried too slowly. Pathologically, red corpuscles vary in size and shape, staining properties, and structure. (1) Variations in Size and Shape (See Plate VIII and Fig. 84).--The cells may be abnormally small (called _microcytes_, 5 µ or less in diameter); abnormally large (_macrocytes_, 10 to 12 µ); or extremely large (_megalocytes_, 12 to 20 µ). Variation in shape is often very marked. Oval, pyriform, caudate, saddle-shaped, and club-shaped corpuscles are common. They are called _poikilocytes_, and their presence is spoken of as poikilocytosis.