Studies of the bacterial flora of the nasopharynx were made in isolated communities in South Alabama and Labrador. The basic flora was determined in both communities. In Alabama an epidemic of common colds was studied. In Labrador cases of sporadic colds and an epidemic of tracheitis were studied.

Gram-negative cocci were found in nearly all normal individuals in moderate numbers. In pathological states there was a suppression of these organisms.

Staphylococci were found in small numbers in about half of the normal individuals. In pathological conditions they disappeared from most of those affected but were found in increased numbers in a few individuals.

Pfeiffer bacilli were absent or present only in small numbers in normal individuals. During the epidemic of colds in Alabama there was an increase in the number of strains recovered and an increase in the relative numbers of the bacilli in each throat. The highest prevalence was found one month after the epidemic had reached its height. In Labrador a similar increase was coincident with an epidemic of tracheitis. During normal periods the majority of the Pfeiffer strains were of the para non-indol-forming type. During epidemic periods the strains recovered were largely true indol-forming B. Pfeifferi.

Hemolytic streptococci were rarely found in normals. During disease prevalence periods they appeared in a small number of persons.

In Alabama, indifferent streptococci resembled the hemolytic streptococci in their distribution. In Labrador they were found to be widely distributed in both health and disease and composed apparently a part of the normal flora.

Green streptococci were found to be widely distributed in fairly large numbers both in health and disease.

Intermediates, or organisms midway between green streptococci and pneumococci, were found in moderate numbers in each series of persons studied. Early in the Alabama epidemic they were present in large numbers in nearly all persons.

Pneumococci were not found in Alabama in normal individuals. The epidemic of colds in Alabama was accompanied by a marked increase in the incidence of these organisms. In Labrador pneumococci seemed to be part of the normal flora as they were generally distributed throughout the community, in many instances comprising a large proportion of the flora of an individual's throat. The Labrador strains of pneumococci were avirulent.

A variety of other organisms such as diphtheroids, Gram-negative rods, and Gram-positive cocci were found in small numbers in many individuals both in health and disease.

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