_a_ ROBERT KOCH ascribes the tuberculin reaction to the increased necrotic process around the tubercle, the histological changes consisting of hyperaemia, exudation and softening. _b_ EHRLICH considers the formation of antibodies an essential feature in the mechanism of reaction. Formation of antibodies takes place in the middle of the three layers encircling the tubercle, the layer damaged by toxins, but not yet rendered incapable of reaction. _c_ WASSERMANN maintains that the antituberculin found in the tuberculous process draws the injected tuberculin out of the circulation to the tuberculous focus. The interaction that takes place between antituberculin and tuberculin results in formation of ferments which digest albumin, resulting in the softening of tissue. Absorption of softened tissue causes fever. _d_ CARL SPENGLER--Toxins in the blood of the tuberculous are kept in check by antibodies. Injected tuberculin unites with antibodies, thus setting the toxins free. Result--autointoxication. _e_ WOLFF-EISNER--Bacteriolysin is present in the organism of the tuberculous, as result of previous infection; bacteriolysin sets free the potent substances of the injected tuberculin; this acts on the body and the tuberculous focus, producing a reaction.[10] TUBERCULIN TESTS I. SUBCUTANEOUS (hypodermic); introduced by Robert Koch in 1890. II. CUTANEOUS; introduced by Von Pirquet in 1907. III. CONJUNCTIVAL (ophthalmic); introduced about the same time by Wolff-Eisner and Calmette in 1907. IV. PERCUTANEOUS (inunction or salve); introduced by Moro in 1908. V. INTRACUTANEOUS (needle track reaction); introduced as a test by Mantoux in 1909. Described previously by Escherich. I. SUBCUTANEOUS TUBERCULIN TEST 1. APPARATUS AND SOLUTIONS NECESSARY: Glass cylinder graduated to cc. 1 cc pipette graduated to 1/10 cc.[11] 10 cc pipette graduated to 1/10 cc.[12] Hypodermic needle suited to the syringe. Two or more 1/2 oz. bottles. 1/2% carbolic acid solution. Normal salt solution. 1 cc. Old Tuberculin. 2. PREPARATION OF APPARATUS: Glass apparatus, syringe and needles boiled before use. Some keep needles and syringe in 95% alcohol. 3. MAKING SOLUTIONS: Tuberculin No. I: Tuberculin No. II: Label one bottle Another _.1 cc. = 1 mg. T_ _.1 cc. = .1 mg. T_ No. I { Put 0.1 cc. T in bottle No. I { Add 9.9 cc. of 1/2% carbolic acid solution { Put 1 cc. of Tuberculin solution from No. II { No. I into bottle No. II { Add 9 cc. of 1/2% carbolic solution In making dilutions you may use your syringe instead of pipette. Dilutions can be kept _one week_ in a dark, cool place. Discard turbid solutions. 4. PREPARATION OF THE PATIENT FOR THE TEST: