In medical practice the reaction is used as a means of diagnosis in certain diseases, such as the tuberculin test in tuberculosis, the mallein test in glanders. The individual or animal with tuberculosis becomes sensitized to certain proteins of the tubercle bacillus and when these proteins in the form of tuberculin are introduced into the body a reaction results, local or general, according to the method of introduction. The practical facts in connection with the tuberculin test are also in harmony with the author’s theory of anaphylaxis as above outlined. Milder cases of tuberculosis give more vigorous reactions because the intracellular enzymes are not used up rapidly enough since the products of the bacillus are secreted slowly in such cases. Hence excess of enzyme is free in the blood and the injection of the tuberculin meets it there and a vigorous reaction results. In old, far-advanced cases, no reaction occurs, because the enzymes are all used in decomposing the large amount of tuberculous protein constantly present in the blood. The fact that an animal which has once reacted fails to do so until several months afterward likewise depends on the fact that the _excess_ enzyme is used in the reaction and time must elapse for a further excess to accumulate. The anaphylactic reaction has been made use of in the identification of various types of proteins and is of very great value since the reaction is so delicate, particularly when guinea-pigs are used as test animals. Wells has detected the 0.000,001 g. of protein by this test. It is evident that the test is applicable in medico-legal cases and in food examination and has been so used. A TABULATION OF ANTIGENS AND ANTIBODIES AS AT PRESENT RECOGNIZED. CLASS OF ANTIGEN ANTIBODY ACTION OF ANTIBODY RECEPTOR Toxin Antitoxin Combines with toxin and I. hence prevents toxin from uniting with a cell and injuring it, _i.e._, neutralizes toxin. Enzyme Antienzyme Combines with enzyme I. and thus prevents enzyme from uniting with anything else and showing its action, _i.e._, neutralizes enzyme. Solution of Precipitin Unites with its antigen II. protein and causes its precipitation from solution. Solution of ? Causes phenomenon of (?) protein anaphylaxis(?)