1. The normal bacterial flora of the nose and throat of thirteen individuals has been studied over periods ranging from 5 to 9 months.
2. Observations have been made of qualitative and quantitative changes in the flora occurring in the course of colds and of throat infections appearing in the group.
3. The normal basic nasal flora includes Staphylococcus albus, diphtheroids, and for certain individuals Staphylococcus aureus and citreus. Occasional transient bacteria are Gram-negative cocci and non-hemolytic streptococci.
4. The normal basic throat flora includes Gram-negative cocci, non-hemolytic streptococci, and for certain individuals "large Gram-positive cocci," B. influenzæ, Bacillus "X," and diphtheroids. Transient organisms are Staphylococcus albus, hemolytic streptococci,Staphylococcus aureus and citreus, and pneumococci.
5. No bacteria were found in early cold cultures to which a causative rôle could be assigned.
6. In the course of colds the basic flora of the nose was often scanty in the early stages. The throat showed reduction of prominence or alterations in predominance of the basic flora.
7. Certain organisms were prominent in colds, usually as late or secondary invaders, these included Staphylococcus aureus, hemolytic streptococci, and B. influenzæ.
8. There was a striking increase in the incidence of hemolytic streptococci in throat infections.