We pointed out, in the section on Immunity (see p. 577), the frequency of relapses in influenza. These relapses generally occur in the following way: One or more days after the fever has disappeared and the patient feels himself convalescent in every other respect, febrile symptoms appear anew, either gradually or suddenly, accompanied by chills, and the symptoms of the initial influenza recur (repetition of the first attack). But the relapse may also develop additional symptoms. If the first attack was only nervous, the relapse may include also catarrhal respiratory symptoms. The contrary condition-that is, respiratory symptoms first and nervous symptoms later-is much rarer. The second attack is often more severe than the first; very frequently under the guise of a relapse of influenza, pneumonia or other inflammatory complications first appear.
The real influenza relapses are due to the germs remaining from the first attack, which suddenly multiply again and subject the incompletely immunized patient to a fresh attack of influenza. Certain bacteriologic investigations make it likely that the germs in convalescence may remain in an attenuated form perhaps for fourteen days or longer in the various cavities of the human subject, and later on again become virulent. But in these late relapses, especially during an epidemic, a new infection is just as probable. Overzealous con tagionists, to save their theory of immunity, have denied these reinfections and have sought to explain these attacks as late relapses or simple coryza. (Compare p. 578.) It is not clear to me how this helps the doctrine of immunity. As far as theory is concerned, it is surely immaterial whether the influenza arises anew, after two to three weeks, from the residual germs (relapse) or from freshly introduced germs (reinfection). In both cases the patient demonstrates that he has not been absolutely immunized by the first attack. [The disease is sometimes continued in the form of chronic influenza, in which the bacilli do not disappear and lead to chronic bronchitis or chronic pneumonia. (See p. 632.) Such cases may have any of or all the symptoms of an acute attack at various and irregular periods, while enjoying comparatively good health in the intervals.-Ed.]