Experiment has shown that animals that have been cured of tetanus possess no immunity whatever against tetanus; nevertheless Behring and Kitasato[122] first, and Wassermann and Kitasato later on, succeeded in preparing a tetanus antitoxin. To obtain this, the immunization of the animal, horse or cow, is effected by injecting increasing quantities of the toxin, more or less attenuated by mixing it with Gramm's iodine solution; the immunization is easily and rapidly accomplished by the process devised by Roux and Vaillard.[123]
The immunized animals yield a serum which, mixed with tetanus cultures, renders these innocuous, and which enjoys an antitoxic power that borders on the marvelous.[124] A quintillionth of a cubic centimeter of the serum per gramme weight of a live mouse suffices to protect the animal from an otherwise fatal quantity of tetanus toxin.[125]
This serum is nevertheless powerless to preserve man in cases of acute tetanus; it confers an immediate, but only transitory, immunity.
As to its mode of action, it appears to cause a permanent condition of excitation or of nutritive reaction of the cells, which makes these resistant to the poison. As in the case of the other toxins, the quantity of antitoxin necessary to protect an organism is so much greater the later the treatment is applied.
Mallein (Toxin of Glanders).—Among the soluble products secreted in the culture media by the glanders bacilli, there are found true toxins to which are ascribed certain symptoms of glanders infection. These toxins have been isolated and designated by the name mallein. First prepared by Helman and Kalmino, mallein was later on specially studied by Roux and Nocard, and, in consequence of the researches of the last-mentioned scientist, it has acquired great importance.[126] It is obtained by sterilizing at 110° C. cultures of the glanders bacillus made with mutton bouillon with the addition of salt, glycerin, and peptones. To isolate the toxin the culture bouillon is first sterilized by heating for half an hour in an autoclave at 100° C. It is then filtered, concentrated to one-tenth its volume on a water-bath, and filtered through a Chardin filter. The mallein is thus obtained in the form of a brown syrupy liquid containing half its weight of glycerin.
This solution keeps well when kept from air, light, and heat. In practice it is employed in 10-per cent. solution in phenolated water (5:1000). The mallein may be precipitated from the crude solution by the addition of alcohol, as recommended by Foth. Foth's mallein occurs as a white, light powder, very easily soluble in water.
Mallein enjoys a very important rôle in veterinary therapeutics, a rôle analogous to that of tuberculin, permitting the diagnosis of incipient glanders.[127]
Experience has shown that in animals already attacked by glanders, even if ever so slightly, the thermic reaction never fails when 0.25 Cc. of the mallein solution is injected. In healthy animals, however, the injection of mallein, even in much larger quantities, causes no apparent effect. In animals attacked by glanders the reaction attains its maximum in twelve hours, and several days are required for the temperature to return to normal.[128]
According to Nocard, mallein possesses no immunizing properties whatever.[129]
Typhoid Toxin.—This is obtained, like the other microbial toxins, from a culture, prepared with more or less difficulty, from Eberth's typhoid bacillus. This toxin, injected into guinea-pigs, develops in them typhoid fever.