1. Anaphylaxis or allergy of rabbits against horse serum can be proved by subcutaneous test.
2. The test is best made in the following way. The skin of the animal, preferably of the abdomen or flank, is shaved. (This should be done a few hours before the injection.) The injection is made by means of a small hypodermic syringe and intradermally. An effort was made not to inject the serum under the skin. Those injections were considered most favorable by which the serum remained as a small bleb in the skin proper. Undiluted horse serum was used for most of the experiments. The amount injected varied from 0.0I cubic centimeter to I cubic centimeter. The reaction seemed as definite after 0.0I cubic centimeter as after a larger quantity.
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3. The specific reaction appears in from twelve to twenty-four hours after the test is made and reaches its maximum in from twenty-four to thirty-six hours. It consists of a local swelling extending from 0.5 to 2 centimeters from the point of inoculation. The skin involved in the raised area is usually red and hotter than the surrounding skin. Macroscopically and microscopically the reacting area has the appearance of a local acute inflammation.
4. The altered reactivity (allergy) or hyper-susceptibility (anaphylaxis) sets in usually in from ten to fifteen days after the first injection of horse serum, and lasts at least three months. Individual rabbits show marked variation from the average time of the development of anaphylaxis.
5. The appearance of precipitines against horse serum in the blood of rabbits appears nearly synchronously with the allergic condition.
6. After large injections of serum the allergic rabbits still react subcutaneously. A suppression of allergy which would correspond to the so-called anti-anaphylaxis could not be proved.
7. Also in regard to the offspring of injected rabbits the subcutaneous test was not positive. The young of these rabbits did not develop a more active allergy than the young of normal rabbits.
8. Neither the injection of considerable quantities of horse serum nor the development of a marked local reaction in the skin after intradermal inoculations of horse serum in a sensitized rabbit is accompanied or followed by greater variations in the number or types of leucocytes in the circulating blood than is found in control animals.