Some recent experiments by J. Martin and Cherry (_Proceedings of the Royal Society_, 1898, LXIII, p. 423) have clearly brought out this fact. These authors made mixtures of serpent venom with its antivenom, which they filtered through a layer of gelatin, under the supposition that, if the venom and its antivenom were not chemically combined, the former alone would be able to pass through into the filtrate, because its molecules are so much smaller. Martin and Cherry allowed the venom and its antivenom to remain in contact for varying periods before filtering. As the result of a series of experiments carried out with this idea, they have demonstrated that the filtrate obtained after allowing a few minutes' contact between the two substances, was decidedly toxic, while that obtained after a contact of half an hour was absolutely non-toxic. From this the authors conclude that the antitoxin enters into chemical union with the venom, but that the combination does not take place immediately, and requires a certain length of time for its accomplishment. Ehrlich and Knorr have demonstrated that the neutralization is less rapid in dilute solutions than in concentrated ones. Prof. Svante Arrhenius has completed our knowledge regarding the mode of combination between the toxins and the antitoxins, by demonstrating the occurrence of limited reactions analogous to the etherification of an alcohol by an acid, and in such a manner that there always exists, in a mixture of these two substances, a certain quantity of free toxin and antitoxin. This is an important modification of the general ideas held in this respect.[49] [49] SVANTE ARRHENIUS: La Physico-chimie des Toxines et des Antitoxines. _Conférences de la Société chimique de Paris_, May 20, 1904. See also MADSEN AND ARRHENIUS: Testkrift red indivulsen of Stotens Serum Institut. Copenhagen, 1902. It appears necessary to bring here more clearly in evidence the fact that _the antitoxin inhibits the noxious action of the toxin, even outside the living organism, by uniting with it to form a compound in identically the same manner as when a strong base and a strong acid are brought together_. As we have seen, all the conditions of environment that favor or retard the formation of salts, in a like sense influence the neutralization of the toxin by its antitoxin.