1. The upper respiratory tract is sterile at birth.

2. In the first 2 weeks of life the infant acquires a basal flora comparable to that of adults except that the potential pathogens are absent.

3. During the ensuing months the potential pathogens may appear without giving rise to symptoms and by 8 months the infant's flora is entirely comparable to the adult's.

4. There is no evidence of a specific bacterial incitant for the first colds of infancy.

5. In infants with recurrent colds, secondary infection of the nose with pneumococci or B. pfeifferi probably plays a part.

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