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In referring to some of the associated conditions of influenza one scarcely knows whether to consider them as complications or sequelæ. The pathological process certainly had its origin from the influenzal attack, but at times apparently assumed an inactive stage. The patient is usually free from any specific influenzal symptoms, but retains for a long time other symptoms referable to various organs, or he may have been normal for a shorter or a longer period and then suddenly develop symptoms apparently independent of the previous infection. It may be well to consider all such conditions which followed the febrile attack, whether immediately or more remotely, as sequelæ, and I shall therefore speak of them as such.

The first and probably the most interesting and confusing are the conditions found in the lungs following influenza. A chronic bronchitis, an old bronchiectasis, or a previous tuberculous lesion in whatsoever stage, may present acute symptoms and signs which are difficult to interpret. The question always arises in the individual case—is this a process due to the recent influenzal attack, or was it there before the attack? Is it of streptococcic, pneumococcic, or tuberculous origin? The history of previous diseases of the lungs may help to arrive at a diagnosis. The history of the severity of the influenzal attack is of very little help, because the apparently mildest attack may be followed by the most profound changes in the lungs, and the gravest attack with a history of definite lung infection may leave the lungs without a trace of the previous pathology. The physical examination is helpful, of course, in determining whether the lesion is at the apices or at the bases, and from this a reasonably safe inference may be drawn as to whether it is from a previous tuberculous lesion or a recent influenzal infection. The Roentgenologist depends almost entirely upon this localization. If the linear striæ are only at the apex, it is probably tuberculous; but if they are only at the base, or also at the base, it is likely to be an influenzal lung. In fact, the Roentgenologist with his present information is ready to admit that it is most difficult to speak definitely of the lungs in these cases. The possibility of confusing the post-influenzal lung with a tuberculous lesion is not peculiar to this epidemic. After the epidemic of 1889 and 1890 the same condition was observed by clinicians. Dr. Roland G. Curtin, of Philadelphia, in 1892 and 1893 conducted a series of clinics at the Philadelphia Hospital, in which he spoke of the “non-bacillary form of phthisis,” and showed case after case which he said might be diagnosed as pulmonary tuberculosis, but because of the recent epidemic and the absence of the tubercle bacillus he diagnosed them as post-influenzal lung.

In the present stage of our knowledge, many of these post-influenzal lungs will not be diagnosed properly until sufficient time is given for either the lung to clear up or the tubercle bacillus to appear in the sputum. We would emphasize the importance at the present time of finding the tubercle bacillus in all suspicious lung lesions before giving a positive opinion as to the tuberculous nature, even though the physical signs are very definite.

Another group of sequelæ is that due to thyroid disturbance, or disturbance of the endocrin system in general. Since the epidemic a number of patients have been seen who noticed an enlargement of a previously normal thyroid gland or greater enlargement of a previously hypertrophied gland. In the same way the symptoms of hyperthyroidism appeared, new in some or a recrudescence in others.

In some of these there was a disturbance of carbohydrate metabolism, as shown by an occasional glycosuria and an increase in the blood sugar, or by a possible disturbance of the suprarenals, as brought out by the administration of adrenalin hypodermatically (Goetsch test). In the application of this test in post-influenzal patients it appeared that the whole endocrin system was in a state of imbalance.

It appears to us not at all improbable that the so-called psychoneuroses of which fatigue, nervousness, irritability and tachycardia play such an important part might also be explained in the same way. These constitute a group of sequelæ which were frequently recognized after previous epidemics, and which are again coming to the foreground.

We are of the opinion, on account of the apparent absence of any specific pathology of the gastro-intestinal tract and its appendages during the attack of influenza, that the sequelæ referred to the digestive system are largely due to exacerbations of previous physiological disturbances or pathological processes. The patient with a previous peptic ulcer has a recurrence of his ulcer. The patient with an infection of the biliary tract has an acute exacerbation, or may have an attack of biliary colic. In fact, there seem to have been many more cases of this kind since the epidemic than before, and most of the patients date the time of the onset from a period soon after recovering from influenza.

Very few, if any, patients in our experience have exhibited sequelæ due to disease of the cardio-vascular or genito-urinary systems. It may be that these will appear later when the more remote effects of an acute infection are recorded.

A very commonplace sequel, but of more or less interest, is the tendency to furunculosis. Our attention was particularly called to the associated hyperglycæmia. The blood sugar readings varied from 0.2 to 0.41. There was no glycosuria, acetone or diacetic acid. We have no explanation to offer for this, although one might dilate readily on many attractive theories. The hyperglycæmia, one may add, was readily reduced by a lowered carbohydrate intake, which also had a curative action on the furunculosis.

Finally we would mention the peculiar epidemic which has been observed apparently over the world, encephalitis lethargica. We do not for a moment put ourselves on record as regarding this disease as a post-influenzal affair, but no one will deny that it has a peculiar time relation to the epidemic; and further, that its distribution is apparently identical. Its bacteriology seems to be unknown. Its local pathology in the mid-brain is not peculiar or at variance with encephalitis produced by known organisms. We have seen five cases; three of whom had had undoubted influenza, while the other two were entirely free from even the slightest suggestion of any type of illness previous to the attack. All of these cases recovered. It has been stated that following the 1890 epidemic a clinical condition was observed in Europe which bears a close resemblance to what has been termed at the present time encephalitis lethargica.