A study of 46 cases of pneumococcus pneumonia has shown that a characteristic response may be elicited by the intracutaneous injection of 0.1 mg. of the somatic C polysaccharide of pneumococcus. During the acute febrile period in patients who recover, the response consists of a delayed erythema which reaches its maximum intensity in 18 to 24 hours. During convalescence the reaction is not demonstrable. In patients in whom the disease is prolonged by complications the capacity of the skin to react persists. In 7 fatal cases the skin failed to react to C polysaccharide.

Parallel studies of the reaction of the patients' serum with C have confirmed and extended the observations of Tillett and Francis on the appearance of the precipitation phenomenon during the acute stages and its disappearance in recovery.

That the cutaneous and serological reactions are not specific for pneumococcus infection is shown by the results in 29 control cases. 8 patients with infectious febrile diseases not of pneumococcus origin gave responses similar to those noted in pneumonia. 2 patients with non-infectious fevers and 18 of 19 normal individuals failed to give either skin or serum reactions.

These observations emphasize the importance of using separate components of the bacterial cell in the interpretation of cutaneous and serological reactions in pneumonia. The parallelism in results of the skin and serum tests in pneumococcus pneumonia with the somatic carbohydrate C, the significance of the reactions in relation to the clinical course and outcome of the disease, and the frequency of occurrence of both reactions in bacterial infections other than those of pneumococcal origin, are discussed.

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