A definite diagnosis regarding the variety of the pneumonia arising in the course of influenza can, as has been previously mentioned, only occasionally be made at the bedside. There is, strictly speaking, but one clinical sign, which points absolutely to the croupous variety, namely, the typical rusty sputum. On the other hand, a purulent sputum does not by any means exclude croupous pneumonia. (See p. 618.) The lobular character of the inflammation and its gradual development to a compact infiltration occur in both the cellular as well as in many of the croupous forms. The acute lobar infiltration is certainly more characteristic of fibrinous pneumonia, but it occurs also in the acute lobular cellular pneumonia.

We are, therefore, at the bedside thrown back on the bacteriologic examination of the sputum. The finding of influenza bacilli in the sputum establishes the disease as influenza. If they alone are found in the sputum and the case is one of pneumonia without rusty sputum, it is probably a true influenza pneumonia due to the bacillus of Pfeiffer. Finding only diplococci or streptococci in the sputum is evidence for the case being respectively croupous or catarrhal pneumonia. [A rapid disappearance of the bacilli from the sputum is often associated with aggravated toxic symptoms.-Ed.]

Even so, the diagnosis is not so simple. One must be careful in drawing conclusions from the bacteriologic appearance of the sputum to determine the character of the pneumonia of influenza. It is sufficient, for example, to call to mind the fact that while Pfeiffer found in the inflamed parenchyma of the lung only the influenza bacillus, in the trachea and the larger bronchi he found a mixture of different varieties of bacteria, streptococci, and diplococci, although even in this situation the influenza germs were regularly in the majority. Probably the opposite condition may also occur: Diplococci and streptococci in the inflammatory areas of the lung, influenza bacilli in almost pure culture in the bronchioles and bronchi, from which the chief amount of the sputum is derived. Thus Albu found in one patient, in the sputum, a pure culture of influenza bacilli, but in the serous pleural effusion, due to a preceding pneumonia, he found a pure culture of streptococci.

Before we discuss more in detail the clinical and pathologic characteristics of the croupous influenza pneumonias, it may be proper to call attention to a fact regarding the question as to the frequency of croupous pneumonia in influenza, which up to now has been almost totally neglected.

Wherever accurate statistics derived from a large amount of material have been tabulated at the time of the influenza pandemic, and wherever an attempt has been made to distinguish between pneumonia caused by influenza and the cases of primary genuine croupous pneumonia occurring during the same period, it has appeared that the frequency of croupous pneumonia increased considerably at the time of the occurrence of an epidemic of influenza.

In my lectures of 1890 I demonstrated this fact with details and convincing statistical curves. Since it was noted everywhere, in Berlin, Vienna, Paris, Cologne, Munich, Marburg, Wiirz burg, Riga, Moscow, Warsaw, and Boston, it cannot have been due to a coincident occurrence of influenza with an epidemic of croupous pneumonia, as some authors assumed at the time of the pandemic, but it proves, on the other hand, that numerous cases of pneumonia during the prevalence of influenza, which, on account of their clinical course and the postmortem examination, were believed to have been genuine croupous pneumonia, were of influenzal origin. From this we infer that influenza more frequently gives rise to true croupous pneumonia by mixed infection than is admitted by many.

Concerning this, Curschmann expressed himself as follows in the meeting at Leipsic above alluded to: " Also the fibrinous pneumonia not complicated with influenza presents an unusual picture during the epidemic." Curschmann too emphasizes the frequency and intensity of the pleurisy accompanying influenza pneumonia.

We would refer our readers to our previous section on Mortality. (See p. 568.) We give here the mortality from pneumonia in Vienna during the time of the pandemic of 1889-1890, according to weeks: The first week in December, 40 cases; second week, 56; third week, 51; fourth week, 124;* first week in January,* 170; second week,* 123; third week, 66; fourth week, 56 cases (according to Drasche). The number of the cases of "genuine croupous pneumonia" which were admitted to the Municipal Hospital at Cologne during the years 1879-1890, during both months of December and January, were as follows, taking the individual years: 1879-1890, 17; 1880-1881, 16; 1881-1882, 19; 1882-1883, 18; 1883-1884, 23; 1884-1885, 35; 1885-1886, 41; 1886-1887, 30; 1887-1888, 32; 1888-1889, 24. On the other hand, during December and January of 1889-1890, at the time of the influenza epidemic, there were 66 cases. These 66 cases of "genuine croupous pneumonia" occurring during the influenza months, December and January, of 1889-1890, are divided among the individual weeks as follows: December 1 to 10, 10 cases; December 11 to 20, 6 cases; December 21 to 31 (the height of the influenza epidemic), 24 cases; January 1 to 10, 16 cases; January 11 to 20, 6 cases; January 21 to 31, 4 cases.

"Genuine" croupous pneumonia was therefore most frequent exactly at the period when the influenza epidemic was at its height.**

According to Shattuck, the general mortality from pneumonia in Boston during the influenza months, December and January, 1889-1890, was double that of the preceding year.

Heryng observed in the Rochus Hospital at Warsaw, during the influenza period, six times as many cases of croupous pneumonia as in the corresponding period of other years.

A further proof that the cases of " primary genuine croupous pneumonia' ' which occurred with increased frequency during the time of influenza were due to influenza is seen in the fact that these " genuine " pneumonias often run an atypical course, both from a clinical and from a pathologic point of view, and, furthermore, were particularly malignant. In this respect they were like the clearly secondary croupous pneumonias, that is, those arising as a complication of influenza. P. Guttmann, Furbringer, Landgraf, A. Vogl (Munich), Krannhals, Marchand, and many others called attention to the marked alteration in character of the "genuine croupous pneumonias" of influenza. We laid stress ourselves on this fact in our lectures of 1889. This fact, furthermore, shows and fully agrees with what was said above, that this presumed "genuine" croupous pneumonia of influenza periods is mostly not a genuine pneumonia, but one caused by influenza infection, that is, a mixed infection representing what we designated "the pneumonic form of influenza."