Fifty-five individuals were tested to determine the pneumococcidal promoting activity of their serum against Types I and II pneumococci. By repeated tests an attempt was made to study the constancy of the degree of their immunity over intervals of 2 to 6 months. In this group were included nine persons with common colds and twelve cases of a severe influenza-like infection. Fifteen of the fifty-five cases showed a change in titer of their humoral immunity against either Type I or Type II or both. Three of these showed an increase, and twelve a decrease. This reaction in most instances was a specific one in that the altered reaction toward one type was not associated with a similar change toward the other type pneumococcus. Colds and influenza-like infections apparently exerted no effect upon the titer of humoral immune substances.

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