[Illustration: FIG. 2.--_Cicuta maculata_ (water hemlock); _A_, upper part of stem with leaves and compound umbels; _B_, base of stem and thick tuberous roots; _C_, cross-section of stem; _D_, flower; _E_, fruit; _F_, fruit in longitudinal section; _G_, cross-section of a mericarp. (From _Applied and Economic Botany_, by courtesy of Professor Kraemer [after Holm].)] Investigators from the New York City Health Department have found that certain cases of alleged "ptomain poisoning" were really due to "sour-grass soup."[21] This soup is prepared from the leaves of a species of sorrel rich in oxalic acid. In one restaurant it was found that the soup contained as much as ten grains of oxalic acid per pint! [Illustration: FIG. 3.--Fly Amanita (poisonous). (_Amanita muscaria_ L.) (After Marshall, _The Mushroom Book_, by courtesy of Doubleday, Page & Company.)] By far the best-known example of that form of poisoning which results from confounding poisonous with edible foods is that due to poisonous mushrooms.[22] There is reason to believe that mushroom (or "toadstool") intoxication in the United States has occurred with greater frequency of late years, partly on account of the generally increasing use of mushrooms as food and the consequently greater liability to mistake, and partly on account of the growth of immigration from the mushroom-eating communities of Southern Europe. Many instances have come to light in which immigrants have mistaken poisonous varieties in this country for edible ones with which they were familiar at home. In the vicinity of New York City there were twenty-two deaths from mushroom poisoning in one ten-day period (September, 1911) following heavy rains. The "fly _Amanita_"[23] (_Amanita muscaria_) in this country has been apparently often mistaken for the European variety of "royal _Amanita_" (_A. caesaria_).[24] Such a mistake seems to have been the cause of death of the Count de Vecchi in Washington, D.C., in 1897.