The lesions of the respiratory tract peculiar to this disease and most frequently encountered are:
An acute tracheobronchitis associated with diffuse involvement of the pulmonary parenchyma.
Hyalinization of the epithelium of the air passages, and necrosis of the alveolar walls with extensive interstitial emphysema and occasionally with pneumothorax.
Dilatation of the terminal bronchioles.
Aplastic serofibrinous, and hemorrhagic, pneumonic exudates.
Necrotizing and organizing bronchiolitis, and pneumonia: lobar, lobular, peribronchial, interstitial.
The sequelæ—obliterating bronchiolitis and bronchiolectasis.
Proliferation of alveolar and bronchiolar epithelium.
The extrarespiratory lesions of influenza are neither constant nor characteristic. Irrespective of localization, they have the same fundamental pathology characterized by:
Vascular damage.