The inaccuracy of clinical diagnosis of the pneumonia of influenza is further illustrated by a consideration of lobar pneumonia. This diagnosis on the one hand was made 136 times and was correct 67 times and incorrect 69 times; on the other hand, lobar pneumonia was found at autopsy 98 times and had been diagnosed in only 67 of these cases (68.4 per cent).
Classification of the Pulmonary Lesions of Influenza.— Influenzal pneumonia exhibits the following noteworthy characters:
1. Acute bronchitis with injury or destruction of lining epithelium and accumulation of inflammatory exudate within the lumen.
2. Hemorrhagic pneumonia with accumulation of blood within the alveoli and within and about the bronchi.
3. Susceptibility of bronchi and pulmonary tissue to secondary pyogenic infection with necrosis and suppuration.
4. Bronchiectasis.
5. Tendency to the occurrence of chronic pneumonia following failure of pneumonia to undergo resolution.
All these changes are doubtless referable to the severity of the primary injury to the lower air passages.
In the presence of destructive changes in the bronchi many bacterial species, including B. influenzæ, pneumococci of various types, streptococci (notably hemolytic streptococci) and staphylococci may invade the lungs and produce acute inflammation. The anatomic characters of the pneumonic lesions following influenza are equally varied.
In order to obtain insight into the pathogenesis of these lesions, it is desirable to imitate the historical development of knowledge concerning the characters and causes of disease, namely, first to define accurately the lesions concerned and later to determine with what microorganisms these lesions are associated. The difficulties of this undertaking are increased by the multiplicity of the microorganisms concerned and by the well-known truth that the same microorganism, e. g., the tubercle bacillus, may produce widely different anatomic lesions.