If the atrium of an infection and its specific etiological agent are
undetermined, the narrator of the pathology of a specific disease is
confronted immediately with serious obstacles in the elaboration of a
complete picture. Some writers assume that the respiratory tract is the
portal of entry in influenza (162), though the specific agent is still
unknown.[2] Whatever the agent, unquestionably it attacks the
respiratory tract at a very early stage in the disease and produces a
lesion which becomes responsible for the most serious aspect of
influenza, whether this phase be primary or only a complication.
Among the lesions which will be considered, therefore, those of the
respiratory tract chiefly will be emphasized. They include the changes
in the large air passages, as well as the pulmonary, alveolar, and
interstitial involvement. Unquestionably, a very close association
exists between the lesions of the larger air passages and those of the
alveoli, but probably it is equally true that the former may occur
alone; in many instances also they are the forerunners of the latter
lesions. Consequently, it seems logical to begin with an exposition of
the lesions in the trachea and its ramifications, including the
bronchioles.