The histology of consolidation which is definitely limited to secondary lobules or groups of lobules varies considerably. When death occurs in the early stage of the lesion, consolidated patches are deep red and somewhat edematous, so that bloody serous fluid escapes from the cut surface of the lung and red blood corpuscles are present in the alveoli in great abundance together with polynuclear leucocytes, fibrin and serum in varying quantity. It is not uncommon to find evidence that the lesion has had its origin in the bronchioles and extended from them to other parts of the lobule. Polynuclear leucocytes may be relatively abundant within and immediately about the bronchioles and alveolar ducts, whereas the intervening alveoli and infundibula are filled with red blood corpuscles among which are polynuclear leucocytes and perhaps some fibrin. It may be evident that bronchiolar pneumonia with hemorrhage into intervening alveoli is in process of transformation into a more diffuse leucocytic pneumonia, for polynuclear leucocytes are making their way from the alveolar wall into the blood-filled lumen and, as the result of the presence of blood, remain for a time close to the lining of the alveolus. When the consolidated lobules have assumed a gray or reddish gray color, polynuclear leucocytes are more abundant and often almost homogeneously pack every alveolus within the boundaries of the lobule. In some instances there is fibrin partially obscured by the presence of leucocytes in great number. Although fibrin is less abundant with bronchopneumonia than with lobar pneumonia, nevertheless in a considerable proportion of instances it is a very conspicuous element of the inflammatory exudate within the bronchioles, alveolar ducts and alveoli. It is unusual to find the alveolar ducts and alveoli uniformly plugged with fibrin containing leucocytes; there is a variegated distribution of exudate which has little resemblance to that of lobar pneumonia. Occasionally (Autopsies 242 and 247) polynuclear leucocytes fill the bronchioles, alveolar ducts and infundibula, whereas the surrounding tributary alveoli contain fibrin and polynuclear leucocytes in moderate number; red blood corpuscles may be present in sufficient number to give a homogeneously red color to the lobular consolidation. In association with lobular pneumonia, fibrin within the lung tissue undergoes certain changes which outline very sharply the alveolar ducts and the other structures usually ill defined in preparations of the lung. A remarkable appearance is produced by the deposit of hyalin fibrin upon the surface of the alveolar ducts and infundibula. This lesion has been described by LeCount.