POISONOUS FISHES. 189 



cation. It has been stated that in India fishes may survive 

 in this condition for more than one season, and that ponds 

 known to have been dry for several years, and to the depth 

 of many feet, have swarmed with fishes as soon as the accu- 

 mulation of water released them from their hardened bed. 



The principal use derived by man from the class of Fishes 

 consists in the abundance of wholesome and nourishing food 

 which they yield. In the Polar regions especially, whole 

 tribes are entirely dependent on this class for subsistence; 

 and in almost all nations fishes form a more or less essential 

 part of food, many being, in a preserved condition, most im- 

 portant articles of trade. The use derived by man from them 

 in other respects is of but secondary importance. Cod- 

 liver oil is prepared from the liver of some of the Gadoids 

 of the Northern Hemisphere, and of Sharks ; isinglass from 

 the swim-bladder of Sturgeons, Sciaenoids, and Polynemoids ; 

 shagreen from the skin of Sharks and Eays. 



The flesh of some fishes is at times, or constantly, 'poison- 

 ous. When eaten, it causes symptoms of more or less intense 

 irritation of the stomach and intestines, inflammation of the 

 mucous membranes, and not rarely death. The fishes, the 

 flesh of which appears always to have poisonous properties, 

 are Clwpm thrissa, Clwpea venenosa, and some species of 

 Scarus, Tetrodon, and Diodon. There are many others which 

 have occasionally or frequently caused symptoms of poison- 

 ing Poey enumerates not less than seventy-two different 

 kinds from Cuba ; and various species of Sphyrmna, Balistes, 

 Ostracion, Garanx, Lachnolcemus, Tetragonwrus, Thynnus, have 

 been found to be poisonous in aU seas between the tropics. 

 All or nearly all these fishes acquire their poisonous proper- 

 ties from their food which consists of poisonous Medusee, 

 Corals, or decomposing substances. Frequently the fishes 



