Much uncertainty exists respecting the conditions under which the various forms of fish poisoning occur. One type is believed to be associated with the spawning season, and to be caused by a poison present in the reproductive tissues. The roe of the European barbel is said to cause frequent poisoning, not usually of a serious sort. The flesh or roe of the sturgeon, pike, and other fish is also stated to be poisonous during the spawning season. Some fish are said to be poisonous only when they have fed on certain marine plants.[30] There is little definite knowledge about the poisons concerned. They are certainly not uniform in nature. The _Fugu_ poison produces cholera-like symptoms, convulsions, and paralysis. It is not destroyed by boiling. The effect of the Greenland shark flesh on dogs is described as being "like alcohol." It is said that dogs fed with gradually increasing amounts of the poisonous shark's flesh become to some degree immune. Different symptoms are described in other fish poisoning cases.[31] FOOTNOTES: [13] _Science_, XV (1902), 1016. [14] _U.S. Dept. of Agric., Div. of Botany, Bull. 20_, 1898. [15] Among the plants that seem to be most commonly implicated in the poisoning of stock are the larkspur (_Delphinium._ _U.S. Dept. of Agric., Bull. 365_, September 8, 1916), the water hemlock (_Cicuta maculata_) and others of the same genus, the lupines (_U.S. Dept. of Agric., Bull. 405_, 1916), some of the laurels (_Kalmia_), and the Death _Camas_ or _Zygadenus_ (_U.S. Dept. of Agric., Bull. 125_, 1915). The famous loco-weed of the western United States (_U.S. Dept. of Agric., Bull. 112_, 1909) is less certainly to be held responsible for all the ills ascribed to it (H. T. Marshall, _Johns Hopkins Hosp. Bull._, XXV [1914], 234). [16] Chesnut, _U.S. Dept. of Agric., Div. of Botany, Bull. 20_, 1898, p. 17. [17] _Ibid._, p. 28. [18] _Ibid._, p. 45. The seeds of the castor-oil bean, which contain a very powerful poison (ricin) allied to the bacterial toxins, have been known to cause the death of children who ate the seeds given them to play with. [19] Mayer, _Deutsche Viertelj. f. öffentl. Ges._, XLV (1913), 12. [20] Cf. an instance of palmolin poisoning, _Centralbl. f. Bakt._, I, Ref., LXII (1914), 210. [21] _Weekly Bull., N.Y. Dept. of Health_, September 16, 1916. [22] Seventy-three species of mushrooms known or suspected to be poisonous are enumerated in a bulletin of the United States Department of Agriculture, Patterson and Charles ("Mushrooms and Other Common Fungi," _Bull. 175_, 1915). This bulletin contains descriptions and excellent illustrations of many edible and of the commoner poisonous species. [23] Used in some places as a fly poison. [24] Ford, _Science_, XXX (1909), 97. [25] Another species of mushroom occurring in this country and commonly regarded as edible (_Panaeolus papilionaceus_) has on occasion shown marked intoxicating properties (A. E. Verrill, _Science_, XL (1914), 408).