The introduction of the leukopenic index as a method of allergic diagnosis is due to the work of Vaughn1on the effect of milk on allergic individuals during the performance of tests for liver function according to the colloidoclastic crisis test of Widal, Abrami and Iancovesco, which is dependent on a fall in blood pressure, a fall in the total leukocyte count, and a prolonged clotting time after the administration of 200 cc. of milk. The pertinent observation was that milk did cause a leukopenia in those patients subsequently found to be sensitive to milk. By repeated tests on a known allergic patient who knew by experience that certain foods were capable of reproducing clinical symptoms on each occasion, the leukocyte response to compatible and to incompatible foods was studied. Those foods producing allergic symptoms were likewise able to depress the total leukocyte count, while compatible foods were in