1. Intracutaneous injection of guinea pigs with an alkaline extract of pneumococcus produces in about two-thirds of the animals an allergy with a skin reaction similar to the allergic skin response of tuberculosis.
2. Continuance of the intracutaneous injections after the appearance of allergy results in its disappearance. The skin ceases to react.
3. Neither the animals manifesting skin allergy nor those which fail to develop it show any significant alteration in susceptibility to pneumococcus infection by intraperitoneal inoculation. Similarly, animals desensitized by continuing the intracutaneous injections after the appearance of allergy show an unaltered susceptibility.