The work reported is a part of the studies on the properties of pneumotoxin and its probable rôle in the pathology of lobar pneumonia. Previous investigators (Clough, Weil, Steinfield and Kolmer) working with dried, autolyzed or heat-killed pneumococci failed to elicit any constant reaction in cases of lobar pneumonia. The present authors used the endocellular hemolytic toxin of the pneumococcus freshly prepared for each test by dissolving the washed living organisms (type I) in solutions of sodium choleate. Guinea-pigs previously sensitized with sublethal doses of pneumotoxin or with the serum or lung exudate of dogs suffering from experimental lobar pneumonia, reacted to the intracutaneous injection of 0.1 cc. of the toxin by a local erythema and hemorrhagic edema in the subcutaneous tissue overlying the muscle. The skin reaction to heat-killed pneumococci was negative in most of these animals and when positive, was of a suppurative type, marked by less edema and more leucocytosis. Control animals gave uniformly negative results.

Among human adult cases of lobar penumonia the reaction (which was characteristically that of a local edema and erythema) was elicited as early as the fifth and as late as the thirteenth day of the disease (two days before and six days after the crisis, respectively). In children it was demonstrable about the same time, but was negative immediately or one or two days after the crisis. Patients recovering by lysis reacted as late as the thirty-second day. In general, the test was positive in all active cases, that is, throughout the toxemia. Cases earlier than the fifth day of the disease were not available. Control patients, suffering with broncho-pneumonia or with acute or chronic infections not of pneumococcic origin, as well as healthy adults and children did not react.

The reaction is regarded as indicative of a state of allergy to pneumotoxin. Sensitization to the toxin presumably takes place with its liberation (by the action of normal body enzymes upon pneumococci normally localized in the lung alveoli) at the time of the prolonged chilling due to exposure. Failure to elicit the reaction during convalescence indicates the establishment of a temporary immunity or the disappearance of the toxin. This skin test does not as yet seem to be of value as a method of serological type diagnosis but may aid in differential diagnosis between appendicitis or tuberculosis and pneumonia (especially in children). It is also of interest because of its bearing on the mechanism of the crisis.

We wish to thank Drs. Stengel, Jenks, Allyn, McCrae, Weiss, Jones, Myer, Wagnez, Hare and other members of the staffs of the University, Children's, Philadelphia General and Jefferson Hospitals for their courtesy and assistance to us during the conduct of these investigations.

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