=Fibrin.=--Increase of fibrin, _hyperinosis_, accompanies the leukocytosis of inflammation and suppuration. It may be approximately estimated on the cover-glass by noting the closeness of the network resulting after fifteen minutes’ exposure. The inflammatory indication of leukocytosis may, therefore, be inferred from its determination, while the leukocytosis of malignant disease will not be so accompanied. Hyperinosis is most marked in pyogenic processes, pneumonia and rheumatism. Its opposite, _hypinosis_, is met with in pernicious anemia. There is no change in the percentage of fibrin in the ordinary anemias or chlorosis. In hemophilia and purpura hemorrhagica the coagulation time is greatly increased. =The Formed Elements of the Blood.=--The specialized elements of the blood which are of particular interest to the surgeon are the red and the white corpuscles. These may both vary in relative size within certain physiological limits. The red cells especially are not of uniform size and vary from 6 to 9 microns in diameter. There are also present in normal blood a small number of red cells having a diameter of only 6 microns, which are known as microcytes. In infancy there are present also so-called giant corpuscles, or megalocytes, with a diameter of 10 microns or more. Considerable variation occurs in disease, especially in the severe anemias. Red corpuscles ordinarily stain with acid dyes, which facilitate their examination and a computation of the number present. When present in unusually large number the condition is spoken of as a _polycythemia_; when in reduced number as _oligocythemia_. In several of the anemias variations in size, shape, and color occur, and in certain of them many of the red corpuscles are found to be nucleated. Red cells which are nucleated are known as _erythroblasts_, and according to their size are spoken of as _microblasts_, _normoblasts_, and _megaloblasts_. Again, under certain diseased conditions the ordinary discoid form of the cells becomes irregular and crenated, and to those which are thus altered is given the name of _poikilocytes_. There is another form of degeneration which consists in death or necrobiosis of the cell, whereby it loses its capacity for staining, or, at all events, stains irregularly and abnormally. This is seen also in cases of severe anemia and in conditions where the blood has been altered by the addition of toxic material, such as chloroform, etc. Occasionally also the red cells show a tendency to a granular change, which is probably entirely degenerative.