[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]
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.
Abrin.—This toxin, which was studied in particular by Warden and Waddell,[52] then by Kobert[53] and de Hellin,[54] is found in the fruit of the Leguminosæ, Abrus precatorius (wild licorice, or jequirity). Its name was given it by Warden and Waddell, who discovered both its toxic nature and the vegetable toxin; the toxin is found only in the seeds. To extract it, the seeds are macerated in water, and the solution filtered and precipitated with alcohol; the precipitate which forms is collected and dissolved in distilled water, from which it is again precipitated by adding powdered ammonium sulphate. The precipitate is then collected and submitted to dialysis in order to eliminate the ammonium sulphate. The abrin so obtained forms an albuminoid substance[55] stable at 100° C., and possessing rotatory power; it liquefies starch paste, and is extremely toxic. One milligramme suffices to kill a rabbit within several hours. It must be observed, however, that, as is the case with all the toxins, abrin acts or kills only after a period of incubation which generally exceeds twenty-four hours.
It is possible to vaccinate an organism so as to withstand a lethal dose of abrin, but it requires quite a long time; it is effected by injecting into a suitable animal very small doses of the substance, and increasing the quantity gradually. Rabbits which have been rendered highly immune towards venoms are capable of resisting without inconvenience doses of abrin which are ordinarily fatal; and the blood serum afforded by them contains a specific antibody for the substance.
Ricin.—This vegetable toxalbumin has been studied particularly by Stillmark,[56] by Dixon,[57] and Thuson.[58] It is found in the seeds of the castor plant; three or four of the seeds suffice to cause a gastroenteritis accompanied by serious symptoms and even by death.
It was first isolated by P. Ehrlich, by treating the seeds with lukewarm water, and precipitating the aqueous solution with alcohol. The toxalbumin is soluble in water, but on boiling the solution, the substance loses in great measure its activity.