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..
This very deadly poison is sometimes found in Helvetia esculenta Persoon (Gyromitra esculenta), particularly in old or decaying specimens. It has been studied and named by Boehm. It is quite soluble in hot water, and in some localities this species of Helvetia is always parboiled - the water being thrown away - before it is prepared for the table. It seems to be quite generally agreed that young and perfectly fresh specimens are free from the poison. As the poison is very violent, however, this plant should be carefully avoided.
The symptoms resemble in a very marked degree those of the deadly phallin, the dissolution of the red corpuscles of the blood being one of the most marked and most dangerous; this is accompanied by nausea, vomiting, jaundice, and stoppage of the kidneys. There is no known antidote for this poison, hence the little that can be done would be similar to that mentioned under phallin.
When poisoning by mushrooms is suspected, one cannot too strongly urge that the services of a competent physician should be secured with the least possible delay.