462 Proceedings of Philosophical Societies. [June, 



April 7. — The commencement of a paper, on the poison of 

 fishes, by Dr. D. J. H. Dickson, was read. 



April 21. — The communication from Dr. Dickson, on the 

 poison of fishes, was concluded. 



By the poison of fishes, Dr. D. does not mean the serious, and 

 sometimes fatal consequences arising from wounds inflicted by 

 the spines of the sting ray and other species of fish ; but those 

 which result from eating certain fish, or parts of fish. The 

 journals of many voyages present us with instances of sickness 

 more or less violent, accompanied by intumescence of the body, 

 and irritating eruptions of the skin, being the consequence of 

 eating certain fish. Often the noxious quality appears to reside 

 in a particular part, especially the liver and intestines, as appears 

 from the circumstance of those persons alone, out of a ship's crew, 

 being thus affected who have eaten these particular parts. It is 

 a matter of common observation that all fish are more wholesome 

 and a more agreeable food before than after spawning ; the fish, 

 in the former case, being in high health and vigour, but in the 

 latter, being sick, emaciated, and their muscular fibre becoming 

 remarkably flabby. The difference between these two states, 

 which in the temperate European climates seldom amounts to 

 more than a difference in the agreeableness of the fish, consi- 

 dered as an article of food, often, in tropical climates, causes 

 the same species to be in the one case a wholesome, and in the 

 other case a very pernicious food. Again, certain species, 

 especially in the West Indies, are observed at the same season 

 to be wholesome in certain situations, and very much the con- 

 trary in others. Thus all the fish on the coast of Barbadoea 

 are said to be safe food, even those which on the coasts of the 

 other islands are deleterious. Examples also have occurred of 

 a ship on one day falling in with a shoal of fish which proved 

 perfectly wholesome, and on the very next day falling in with a 

 second shoal of the same species which were found to be 

 poisonous. 



The cause of these differences it is not very easy to ascertain. 

 The common test among seamen of the safety or hazard in feed- 

 ing on any suspected or unknown kind of fish, is to put a piece 

 of silver into the boiler together with the fish, and if the silver 

 acquires a coppery colour the fish is considered as unwhole- 

 some. The coppery, or rather brassy colour thus produced, has 

 probably been the reason why the flavour of fish in this state 

 has been attributed to copper, with which they have been 

 supposed to be infected by feeding on banks of copper ore. But 

 the discoloration of the silver is probably owing to sulphuretted 

 hydrogen, and it is a well-known fact that the drainings of a 

 copper mine are so peculiarly noxious to fish that many lakes, 

 formerly abundantly stocked, have been entirely depopulated by 

 this very circumstance. Vegetable poisons swallowed by the 

 indiscriminate voracity of this class of animals, have been con- 



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