PARASITES AND DISEASE (VEGETABLE PARASITES) 159 



Etiology. The exciting cause of this disease is the 

 Diplococcus pneumoniae, its presence having been de- 

 monstrated in a large proportion of the cases investigated. 

 That predisposing causes and the virulence of the germ 

 are factors in the causation of the disease is shown by 

 the fact that the germ is found in the air-passages of 

 healthy individuals. Of predisposing causes, age plays 

 an important part, the majority of cases occurring in 

 infancy and old age. Lowered vitality from exposure, 

 overwork, poor food, alcoholism, previous debilitating 

 diseases, as influenza, typhoid, etc., injuries to chest, 

 and ether-anesthesia are also predisposing factors. 



Morbid Anatomy. In this disease, instead of isolated 

 areas, the entire lobe of the lung is affected. The in- 

 flammatory process is divided into four stages, which are 

 designated as engorgement, red hepatization, gray he- 

 patization, and resolution. 



Engorgement. In this stage of the disease the lung 

 tissue is deep red in color, the capillaries are dilated and 

 tortuous. The alveoli contain red blood-corpuscles, 

 round cells, and detached epithelial cells, but are not as 

 yet completely occluded. 



Red Hepatization. In this stage the surface shows 

 the indentation of the ribs. Its consistency is firm and 

 friable. The alveoli are completely filled with fibrin, 

 red and white blood-cells, epithelium, bacteria, and 

 granular debris. The bronchial mucous membrane is 

 reddened and engorged, the smaller bronchi often con- 



