DISEASES OF THE RESPIRATORY SYSTEM. 135 



First Stage. — Congestion, engorgement, or hijpercemia. 



Usually the antero-inferior part of the lung is involved, the 

 disease extending upward and backward. 



The lung is of a deep-red color, somewhat firm to the feel, 

 and more solid; it crepitates somewhat, floats in water, but not as 

 well as normally. 



On section, the surface exudes a thin, albuminous, and bloody 

 fluid. 



Second Stage. — Exudation or red hepatization. 



The lungs look somewhat like liver tissue. 



If you open the thorax, the lungs look swollen; they do not 

 collapse, and often the markings of the ribs can be seen. 



The lung is solid, does not contain air, and sinks immediately 

 if thrown in water. 



The air-cells are filled up by the exudation, which consists 

 of a viscid, fibrinous fluid, mixed with red and white cells, which 

 rapidly coagulates, enclosing the corpuscles and completely filling 

 the alveoli. 



On section, the surface is dry, of a reddish -brown color, and 

 granular. 



The exudate becomes prominent, sticks out, and gives this 

 granular appearance. 



The lung tissue is very easily torn; the finger can be thrust 

 into it, and it tears readily. 



Hepatization is not general over the lung; it usually consti- 

 tutes one-third or one-half of one lung. 



Some few cases may involve both lungs, when it is called 

 double or bilateral pneumonia. 



Most cases are unilateral — that is, a part of one lung being 

 involved. 



Third Stage. — Gray hepatization, resolution. 



There is no line of demarcation between the second and third 

 stages; the change is more or less gradual from a red-brown color 

 to a grayish white. 



The surface is more moist, the lung is more friable, the plugs 

 of exudation are less distinct, the lungs present a marbled appear- 

 ance, there being less red blood-cells and fibrine, and more leuco- 

 cytes. The lung does not crepitate, sinking immediately in water. 



If resolution is retarded, part of the exudation undergoes pu- 

 rulent transformation, the color changes to a greenish yellow, pus- 



