Plate XXXII. Contagious pleuropneumonia. This illustrates what are called infarctions. The right half of the figure shows nearly normal lung tissue. The left represents a blackish mass, in which the lung tissue is filled with blood and solidified. This is caused by the plugging of the vein carrying away the blood from this portion. The heart forces the blood through the artery into the tissue at considerable pressure, but owing to the fact that its return is prevented, the minute blood vessels rupture and the air vesicles become distended with blood, which coagulates and causes the firmness of the tissue.