230 Dr Davy's Observations on Fish, 



If the exemption be mainly owing to diet, and that a fish 

 diet, it may be presumed that there enters into the composi- 

 tion of fish, some element not common to other kinds of food, 

 whether animal or vegetable. This I believe is the case, 

 and that the peculiar element is iodine. 



I may briefly mention, that in every instance in which I 

 have sought for this substance in sea-fish, I have found dis- 

 tinct traces of it, and also, though not so strongly marked, 

 in the migratory fish, but not in fresh-water fish. The trials 

 I have hitherto made have been limited to the following, viz., 

 the Red Gurnet, Mackerel, Haddock, Common Cod, Whit- 

 ing, Sole, Ling, Herring, Pilchard, Salmon, Sea-Trout, Smelt, 

 and Trout. In each instance, from about a quarter-a-pound 

 to a pound of fish was dried and charred, lixiviated, and re- 

 duced to ashes, which were again washed. From the sea- 

 fish, the washings of the charcoal afforded a good deal of 

 saline matter on evaporation ; the washings of the ash less. 

 The saline matter from both consisted principally of common 

 salt, had a pretty strong alkaline reaction, and with starch 

 and aqua regia afforded, by the blue hue produced, clear 

 proof of the presence of iodine. In the instance of the fresh- 

 run Salmon, Sea-Trout, and Smelt, a slight trace of iodine 

 was thus detected ; in the spent Salmon descending to the 

 sea, only a just perceptible trace of it was observable, and 

 not a trace of it either in the Parr or in the Trout. 



That iodine should enter into the composition of sea-fish, 

 is no more perhaps than might be expected, considering 

 that it forms a part of so many of the inhabitants of the sea 

 on which fish feed ; — to mention only what I have ascer- 

 tained myself, — in the common Shrimp I have detected it in 

 an unmistakeable manner, and also in the Lobster and 

 Crab, and likewise in the common Cockle, Mussel, and Oyster. 



The medicinal effects of cod-liver oil, in mitigating if not 

 in curing pulmonary consumption, appear to be well esta- 

 blished. And as this oil contains iodine, the analogy seems 

 to strengthen the inference that sea-fish generally may be 

 alike beneficial. 



Should further inquiry confirm this conclusion, the prac- 

 tical application of it is obvious; and fortunately, should 



