PNEUMONIA, MENINGITIS AND GONOKEHEA 323 



produced from certain carbohydrates. Cultures lose their 

 viability relatively quickly. When the organism is sus- 

 pended in broth or physiological salt solution it readily 

 undergoes autolysis or self-digestion. 



Pathogenesis. — The pneumococcus was first described 

 as an organism present in sputum in healthy individuals, 

 which when injected into a mouse, produced a quickly fatal 

 type of septicemia. Later it was found quite consistently 

 associated with acute infectious pneumonia in man and in 

 certain animals, particularly the horse. In pneumonia the 

 organisms are present in the lung tissue causing severe local 

 inflammation. The blood vessels become engorged and 



Fig. 64. — DiPLOCOccus pneumoniae. 



blood plasma is poured out into the air sacs or alveoli. The 

 fibrinogen is converted into fibrin and the alveoli become 

 filled with fibrin clots. Lung tissue which has been changed 

 in this fashion is no longer spongy and capable of floating 

 upon water, but is dense and when placed in water sinks to 

 the bottom. Such lung tissue is said to have undergone 

 hepatization, that is, it has become liverlike in consistency. 

 In some cases there is more or less diffused bleeding into the 

 tissues and they become red. Such a condition is known as 

 red hepatization. When white blood cells are present in 

 great numbers, the lungs are said to have undergone gray 

 hepatization. The organisms may also gain entrance to the 



