This section is from the book "Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc.", by George Francis Atkinson. Also available from Amazon: Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc..
The exact chemical nature of this extremely toxic substance is not certainly known, but it is generally conceded to be of an albuminous nature. That it is an extremely deadly poison is shown by the fact that .0015 grain per 2 lbs. weight of the animal is a fatal dose for cats and dogs. It is the active principle of the most deadly of all mushrooms, the Amanita phalloides, or death-cup fungus. We quote again from Mr. Chestnut's account of phallin and its treatment: "The fundamental injury is not due, as in the case of muscarine, to a paralysis of the nerves controlling the action of the heart, but to a direct effect on the blood corpuscles. These are quickly dissolved by phallin, the blood serum escaping from the blood vessels into the alimentary canal, and the whole system being rapidly drained of its vitality. No bad taste warns the victim, nor do the preliminary symptoms begin until nine to fourteen hours after the poisonous mushrooms are eaten. There is then considerable abdominal pain and there may be cramps in the legs and other nervous phenomena, such as convulsions, and even lockjaw or other kinds of tetanic spasms. The pulse is weak, the abdominal pain is rapidly followed by nausea, vomiting, and extreme diarrhoea, the intestinal discharges assuming the "rice-water' condition characteristic of cholera. The latter symptoms are persistently maintained, generally without loss of consciousness, until death ensues, which happens in from two to four days. There is no known antidote by which the effects of phallin can be counteracted. The undigested material, if not already vomited, should, however, be removed from the stomach and intestines by methods similar to those given for cases of poisoning by Amanita muscaria.
"After that the remainder of the poison, if the amount of phallin already taken up by the system is not too large, may wear itself out on the blood and the patient may recover. It is suggested that this wearing-out process may be assisted by transfusing into the veins blood freshly taken from some warm-blooded animal. The depletion of the blood serum might be remedied by similar transfusions of salt and warm water."