1. In our examinations, only 38 per cent. of the infections of the respiratory tract below the glottis were pure, and this percentage was reached only by carefully following Kitasato's method of handling sputa.

2. Lobar pneumonia may produce sputum free from pneumococci, and may undoubtedly be caused by organisms other than thepneumococcus.

3. There is found a marked yearly variation in the organisms which excite inflammation of the respiratory tract.

4. Micrococcus catarrhalis is usually considered a common secondary invader; but it may, and probably frequently does, assume pathogenic properties.

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