_Decrease of hemoglobin_, or _oligochromemia_, is very common and important. It is the most striking feature of the secondary anemias (p. 204). Here the hemoglobin loss may be slight or very great. In mild cases a slight decrease of hemoglobin is the only blood change noted. In very severe cases, especially in repeated hemorrhages, malignant disease, and infection by the worms uncinaria and bothriocephalus latus, hemoglobin may fall to 15 per cent. Hemoglobin is always diminished, and usually very greatly, in chlorosis, pernicious anemia, and leukemia. {143} _Estimation of Hemoglobin_.--There are many methods, but none is entirely satisfactory. Those which are most widely used are here described. * * * * * [Illustration: FIG. 65.--Von Fleischl's hemoglobinometer: _a_, Stand; _b_, narrow wedge-shaped piece of colored glass fitted into a frame (_c_), which passes under the chamber; _d_, hollow metal cylinder, divided into two compartments, which holds the blood and water; _e_, plaster-of-Paris plate from which the light is reflected through the chamber; _f_, screw by which the frame containing the graduated colored glass is moved; _g_, capillary tube to collect the blood; _h_, pipet for adding the water; _i_, opening through which may be seen the scale indicating percentage of hemoglobin.] (1) Von Fleischl Method.--The apparatus consists of a stand somewhat like the base and stage of a microscope (Fig. 65). Under the stage is a movable bar of colored glass, shading from pale pink at one end to deep red at the other. The frame in which this bar is held is marked with a scale of hemoglobin percentages corresponding to the different shades of red. By means of a rack and pinion, the color-bar can be moved from end to end beneath a round opening in the center of the stage. A small metal cylinder, which has a glass bottom and which is divided vertically into two equal compartments, can be placed over the opening in the stage so that one of its {144} compartments lies directly over the color-bar. Accompanying the instrument are a number of short capillary tubes in metal handles. Having punctured the finger-tip or lobe of the ear as already described, wipe off the first drop of blood, and from the second fill one of the capillary tubes. Hold the tube horizontally, and touch its tip to the drop of blood, which will readily flow into it if it be clean and dry. Avoid getting any blood upon its outer surface. With a medicine-dropper, rinse the blood from the tube into one of the compartments of the cylinder, using distilled water, and mix well. Fill both compartments level full with distilled water, and place the cylinder over the opening in the stage so that the compartment which contains only water lies directly over the bar of colored glass.