To the eminent German chemists Schmiedeberg and Koppe is due the credit of isolating the active poisonous principle of the Fly mushroom (muscarin). These authors published in 1869 a series of interesting experiments made with muscarin, having relation to its effect upon the heart, respiration, secretions and digestive organs, etc., and this was supplemented by other experiments made by their pupils, Prof. R. Boehm and E. Harnack. Schmiedeberg and Koppe's work relates to the effect of this poison on man as well as upon the lower animals. Dr. J. L. Prevost in 1874 reviewed the investigations made by Schmiedeberg and Koppe in a paper read before the Biological Society of Geneva, adding some confirmatory observations of his own relative to experiments made with muscarin upon the lower animals. The experiments made by these authors demonstrated "that muscarin arrests the action of a frog's heart, that a muscarined frog's heart began to beat immediately under the influence of atropin, and further that it was impossible to muscarine a frog's heart while under the influence of atropin."

Schmiedeberg subjected cats and dogs to doses of muscarin, large enough to produce death, and when the animals were about to succumb, injected hypodermically from one to two milligrams of sulphate of atropin, after which the toxic symptoms disappeared and the animals completely revived. Prof. Boehm found that digitalin likewise re-established heart action when suspended by the action of muscarin.

In man the fatal termination, in cases of mushroom poisoning, where the antidote is not used, may take place in from 5 to 12 hours or not for two or three days.

According to Prof. E. Kobert's recent chemical analysis, the "Fly mushroom," Amanita muscaria, contains not only the very poisonous alkaloid muscarin and the amanitin of Letellier (cholin), but also a third alkaloid, pilz atropin. The pilz-atropin (mushroom atropin) was discovered by Schmiedeberg in a commercial preparation of muscarin, and later Prof. Kobert discovered it in varying proportions in fresh mushrooms of different species. The effect of this third alkaloid, it is claimed, is to neutralize to a greater or less extent the effect of the poisonous one. Under its influence, when present in quantity, the poison is almost entirely neutralized. Contraction of the pupils changes to dilation, and slowing of the pulse may disappear. Only through the presence of this natural antidote in the Fly mushroom, says Kobert, is it possible, as in some parts of France and Russia, to eat without danger this mushroom, which contains 10% of sugar (trehalose or mycose) in a fermented and unfermented condition. He states also that delirium, intoxication, and other symptoms which, according to Prof. Dittmer of Kamschatka and various scientific travellers, are reported effects of the Fly mushroom in the extreme north, are not experienced in the same degree in southern Russia. This difference in action, he thinks, may be very properly attributed to the varying proportion of the above-mentioned atropin in the mushroom or to the presence of substances which develop only in the extreme north.

The symptoms of muscarin poisoning, apart from vomiting and purging, are slowing of the pulse, cerebral disturbance, contraction of the pupils, salivation and sweating. In case of death, which is caused by suffocation or a suspension of heart action, the lungs are found to be filled with air, and there is a transfusion of blood in the alimentary canal.

Prof. R. Kobert, in a lecture delivered before the University of Dorpat in 1891, states that muscarin is found equally in the Fly mushroom (A. muscaria), the Panther mushroom (A. pantherinus), Boletus luridus, and in varying quantities in Russula emetica. He states also that though highly poisonous to vertebrates, muscarin is not so to flies, and that the noxious principle in A. muscaria which kills the flies is not as yet determined.

It has been shown that the lower animals, such as sheep and geese, as well as man, have been severely poisoned by feeding on the "Fly mushroom," and that in the case of the horse, experiments have demonstrated that even 0.04 of a gramme, 0.62 of a grain, have caused marked symptoms of poisoning.

For muscarin as for neurin poisoning the antidote is atropin administered internally or by subcutaneous injection.