more recent experiments of Wagner (1890). According to Canalis and Morpurgo, pigeons which are enfeebled by inanition easily contract anthrax as a result of inoculation. Arloing states that sheep which have been freely bled contract anthrax more easily than others; and Serafini found that when dogs were freely bled, the bacillus of Friedlander, injected into the trachea or the pleural cavity, entered and apparently multiplied to some extent in the blood, whereas without such previous bleeding they were not to be found in the circulating fluid. Again, the simultaneous injection of certain chemical substances may overcome the vital resisting power of the tissues or fluids of the body in such a way that infection and death may occur as a result of inoculations into animals which have a natural or acquired immunity against the pathogenic micro-organisms introduced. Thus Arloing, Cornevin, and Thomas have shown that rabbits succumb to symptomatic anthrax when lactic acid is injected at the same time with the bacillus into the muscles. Nocard and Roux have obtained the same result by injecting various other substances, and their experiments show that the result is due to the injurious effects of the substance injected upon the tissues, and not to an increased virulence on the part of the pathogenic bacillus. The experiments of Leo are of a similar nature. By injecting phloridzin into rats he caused them to lose their natural immunity against anthrax. Certain anaesthetic agents have also been shown to produce a similar result. Platania communicated anthrax to immune animals—dogs, frogs, pigeons—by bringing them under the influence of curare, chloral, or alcohol; and Wagner obtained a similar result in his experiments on pigeons to which he had administered chloral.
In view of the results of recent experimental researches which show that, in certain cases at least, acquired immunity depends upon the formation of an antitoxine in the body of the immune animal, we are convinced that the theory of immunity under discussion, first proposed by the writer in 1881, can not be accepted as a sufficient explanation of the facts in general. At the same time we are inclined to attribute considerable importance to acquired tolerance to the toxic products of pathogenic bacteria as one of the factors by which recovery from an infectious disease is made possible, and subsequent immunity established. Of course, when we ascribe immunity to the "vital resistance" of the cellular elements of the body, we have not explained the modus operandi of this vital resistance or "reactive change," but have simply affirmed that the phenomenon in question depends upon some acquired property residing in the living cellular elements of the body. We have suggested that that which has been acquired is a tolerance to the action of the toxic products produced by pathoge-