The termination of influenza pneumonia by a true crisis is unusual; resolution is often delayed for some time. Pseudocrises, viz., a fall of temperature lasting one or even several days, with subsequent exacerbations, frequently occur. This is true not only of the catarrhal variety, but also of the true croupous form.

Occasionally the compact lobar infiltration persists with total dulness and pure bronchial breathing without rales, or only with crepitation, and lasts much longer than in ordinary pneumonia. (Compare p. 627.)

But more frequently resolution of the lobar infiltration occurs, the percussion note again becomes clear, while many, often metallic, coarse rales are heard over the whole lobe. Yet this condition does not improve: for weeks this same physical condition may persist; the sputum is purulent, often simulating the sputa occurring in tuberculosis, and occasionally containing blood; irregular, generally intermittent, occasionally "hectic " febrile fluctuations, with sweating accompany the process of delayed resolution; this is the protracted or "chronic influenza pneumonia." It is self evident that when the process is situated in the upper lobe, there will be a strong suspicion of a possible tubercular affection, especially when we have to deal with weak individuals with hereditary taint or with such as have previously shown signs of tuberculosis. In such cases frequent examination of the expectoration for tubercle bacilli is of decisive importance. Graves called attention to the difficulty of differentiation between chronic influenza pneumonia and pulmonary tuberculosis in the epidemic of 1837, and at the same time pointed out the unusual frequency with which the upper lobes are affected in influenza pneumonia. Teissier, Chatin, and Collet classified these cases in a particular group of influenza, which they called "forme pseudo phy mique," and they describe many illustrative cases. These cases of protracted chronic influenza pneumonia sometimes terminate in the indurative condition described by Kunclrat and Weichselbaum (indurative or chronic interstitial pneumonia). Nevertheless, it is well in practice not to' assume prematurely the existence of this condition, since we know from numerous cases that after many weeks or even months resolution may take place. But in other cases there are permanent and slowly progressive changes terminating in chronic interstitial indurative pneumonia, with connective tissue changes of large portions of the lung, and the formation of bronchiectatic cavities; and by the action of streptococci and staphylococci purulent necrotic and ulcerative processes may also occur.

We had the opportunity of observing two such cases from the time of the acute attack up to their fatal termination two years later.

Again and again the question of tubercle was discussed; the physical signs, the sputa, the temperature curve, and the general appearance of the patient were all in its favor, but the entire absence of tubercle bacilli from the expectoration made us adhere to our diagnosis of chronic indurative and ulcerative pneumonia caused by influenza. The postmortem examination completely confirmed this diagnosis. It is true the lung had a certain amount of induration similar to a tubercular lung, but there were no tubercles, and the microscopic examination proved the absence of tuberculosis. Analogous cases, partly with and partly without postmortem examination, have been described by Teissier, Finkler, and Netter. The latter in a case lasting for fourteen months proved the influenzal nature of the chronic pneumonia by the constant finding of Pfeiffer's bacillus in the sputum and the absence of the tubercle bacillus. Pfeiffer, too, in such cases of chronic indurative pneumonia obtained the influenza bacilli in cover glass preparations.

On the other hand, quite a number of cases occur in which true tuberculosis arises from the chronic influenza pneumonia. After the tubercle bacillus has been sought for in vain in the sputum for weeks it suddenly appears, and then the tubercular affection dominates the clinical situation until the case terminates. The question of Netter, "Must one not admit that grip can give rise to pulmonary tuberculosis?" has received an affirmative reply in a number of cases observed by us in which influenza has been followed by pulmonary tuberculosis. In most of such cases there may have been a latent tuberculosis, which the influenza attack, and particularly the pneumonia, enabled to manifest itself; in other cases the chronic grippal pneumonia may have prepared the soil for the tubercle bacilli.

The fact that influenza not rarely, and then generally by way of protracted pneumonia, leads to tuberculosis of the lungs, was known to the older writers and was emphasized by Fr. Hoffmann (1709), by Canstatt, Biermer, Lebert, Ziilzer, and in our pandemic by Bouchard, A. Vogl, the German army reports, etc. R. Pfeiffer assumes that "the influenza pneumonia, when it affects lungs which have been previously affected by tubercle, may terminate directly in caseation."

A fact that has been substantiated by numerous observations contained in literature, as well as by statistics, is the frequency with which influenza pneumonia terminates in abscess formation and gangrene.

Weichselbaum and R. Pfeiffer, having described certain round cell infiltrations in the peribronchial and intra alveolar connective tissue, because associated with necrosis and purulent infiltration, as "smallest abscesses," it is not surprising that under similar conditions large abscesses occasionally arise ("purulent bronchopneumonia"). Ribbert, Marchand, and others also emphasize this tendency of influenza pneumonia to necrosis and abscess formation. But true croupous pneumonia also not seldom terminates in this manner. Zenker saw an abscess of the lung originate from a fibrinous pneumonia, and Rhyner's three cases of gangrene all developed from croupous pneumonia. In my influenza lectures of the spring of 1890 I reported five cases of abscess and two cases of gangrene of the lung following influenza pneumonia, and drew attention to the remarkable fact that all these seven cases occurred in juvenile individuals, the youngest being a boy of seven years. P. Guttmann, in postmortem examination of sixteen supposed genuine croupous pneumonia cases during the influenza epidemic, found large abscesses in two cases, this being a further proof of the correctness of our previous assertion that numerous cases of croupous influenza pneumonia were thought to be of the genuine variety. (Compare p. 617.)

In the pus from the abscesses diplococci, streptococci, and staphylococci were generally found. In one case P. Hitzig found the specific influenza bacillus.

We will not further consider the clinical signs of the abscess, the occasional perforation into a bronchus combined with copious evacuation of pus, and the consequent protracted indurative processes with cavity formation; neither will we consider the clinical and pathologic conditions of gangrene of the lung. It need hardly be mentioned that the latter occasionally ends fatally with severe hemorrhage or by perforation into the pleural cavity, giving rise to pneumothorax.

Nevertheless I should like briefly to mention two cases observed by me where, in healthy young individuals, sudden and complete pneumothorax of one side occurred at the height of the influenza attack, simultaneously with severe paroxysmal cough. A postmortem examination in both cases showed the condition of pulmonary hyperemia above described, but not a trace of pneumonia, still less gangrene, abscess, or even small necrotic areas. Even on inflating the totally collapsed lung the perforation could not be found. We must suppose that the tumultuous paroxysms of coughing, aided by the hyperemia of the lung, caused a vesicular or subpleural emphysema, and that the pneumothorax was due to the rupture of such an emphysematous vesicle. This was a pneumothorax, due, as its simple nature at the postmortem examination showed, to a pure and simple perforation of gas, as not infrequently occurs also in abscesses of the stomach, intestines, and appendix.

That influenza pneumonia may give rise to pneumothorax without gangrene or abscess formation by means of a circumscribed small pleural necrosis is shown by the observations of Mosler and Albu.