In the vaccinated animal the antitoxin is reproduced, and it is possible to obtain several times, from the vaccinated animals, successive portions of antitoxic serum.[50] The protective power of these antitoxins is absolutely marvelous. An animal accustomed gradually to the tetanic virus yields a serum containing an antitoxin a thousand times more active than the virus. [50] CH. SALMONSEN et TH. MADSEN: Réproduction de la substance antitoxique. _Ann. Inst. Pasteur_, XII, p. 762. ROUX et VAILLARD: _Ibid._, 1893, p. 83. According to Vaillard, a quintillionth of a cubic centimeter of this antitetanic serum suffices to preserve one gramme of living mouse from the effects of a dose of tetanic serum that would otherwise be surely fatal. In the animal, the antitoxins are eliminated mostly by the fluids of the body, and particularly by the urine. Ehrlich has demonstrated that they also pass into the milk, and this fact is confirmed by a large number of observers. It explains the immunity acquired by nurslings, and which is transmitted by the milk. =Serotherapy.=--The search for antitoxins and their rôle in the etiology of infectious diseases are fundamental points in actual therapy. It has been demonstrated that the serums of certain vaccinated animals enjoy very extended antitoxic therapeutic properties; for instance, the serum of vaccinated rabbits is an antivenom towards erysipelas; and the sterilized cultures of the pneumococcus or of the Bacillus pyocyaneus prevents infection of carbuncle (anthrax). The antivenomous serum of the ass immunized by injections of increasing doses of the venom of the terrible naja is a perfect prophylactic and curative, not only as regards the venom of this serpent, but also against that of the crotalus, trigonocephalus, and viper. We shall take up the study of serotherapeutics in another volume of this collection. PART II. _THE TOXINS PROPER._ CHAPTER III. I. VEGETABLE AND ANIMAL TOXINS. The vegetable toxins possess the characteristic property of being innocuous, and of being almost completely devoid of poisonousness, when they are absorbed by the intestines; we can see, from this, how greatly they differ from the poisons proper.[51] [51] It is understood that the active principles of mushrooms are not comprised under this definition, but they will be studied under the next heading. The vegetable toxins known are quite numerous; nevertheless our knowledge regarding them is very incomplete. Our review of them will be chiefly descriptive. Many of the leguminous plants are poisonous, either because of emanations exhaled by them, or by reason of their alkaloids, or because of some toxins contained in them. We shall commence with these.