A series of experiments are reported which illustrate and characterize an altered state of reactivity of the skin of the hypersensitive rabbit to epinephrine (and norepinephrine). The requirements for the production of the lesion are: a state of hypersensitivity, circulating antigen and antibody and focal deposition of epinephrine or norepinephrine. The size and intensity of the reaction appear to be directly related to the amount of epinephrine injected (within certain limits) and to the degree of hypersensitivity as measured by the Arthus reaction. Although circulating antigen is required, the precise quantity does not seem to be as critical as does the amount of circulating antibody; a certain minimum amount is necessary, however. Experimental evidence is given which indicates the utilization of antigen in the production of the lesion. Data tending to identify this lesion with the Arthus reaction are given. The possibility of an analogous relationship between the mechanism of this experimental lesion and the necrotizing arteritis of the collagen diseases is postulated.

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