The trials he made were limited to red gurnard, mackerel, haddock, common cod, whiting, sole, ling, herring, pilchard, salmon, sea-trout, smelt, and trout.
The experiment was as follows.—He dried and charred, lixiviated, reduced to ashes, and again washed from a quarter of a pound to a pound of fish.
A good deal of limy matter was afforded from the washings of the charcoal of the sea fish.
The saline matter was principally common salt, had a pretty strong alkaline reaction, and by the blue hue produced by starch and aqua regia, afforded a clear proof of the presence of iodine. Only a slight trace was detected in the fresh-water salmon, sea-trout, and smelt. In the spent salmon descending to the sea, only just a perceptible trace was observable, and no trace in either parr or trout.
Dr. Davy states further, that he has detected it in an unmistakable manner in the common shrimp; also in the cockle, mussel, oyster, crab, &c.; nor is this remarkable, considering that it enters into the greater part of the food of fishes.
He observes, also, that cod liver oil is well established as an alterative or cure of pulmonary consumption, and as this oil contains iodine, the inference is, that sea fish, generally, may be alike beneficial. The practical application of this inquiry is obvious. A suggestion is also made as to the efficacy of drying fish, even without salt, the drying being complete to the exclusion of even hydroscopic water, for the use of the explorer and traveller.
The inference as to the salutary effects of fish depending on the presence of iodine, in the prevention of tubercular disease, might be extended to goitre, which it is known has already yielded to iodine. This formidable complaint appears to be completely unknown to the inhabitants of sea-ports and sea-coasts. Respecting another and concluding question, viz., the different parts of fish, it is to be remarked that, so far as experiments have gone, the effects will not be the same from all parts of the fish, because the inorganic elements are not the same. The examples chosen are the liver, muscle, roe, or melt. In the ash of the liver and muscle of sea-fish, Dr. Davy always found a large proportion of saline matter, common salt, abounding, with a minute portion of iodine, rather more in the liver than the muscle, and free alkali, or alkali in a state to occasion an alkaline reaction, as denoted by test-paper; whilst in the roe or melt there has been detected very little saline matter, no trace of iodine, nor of free alkali; on the contrary, a free acid, viz., phosphorus, analogous to what occurs in the yolk of an egg, and in consequence of which it is very difficult to digest either the roe or melt of a fish, or the yolk of an egg. The same conclusion on the same ground is applicable to fresh-water fish, viz., the absence of iodine.
A very common North American dish is chowder, which is thus prepared:—
Fry brown several slices of pork; cut each fish into five or six pieces; flour, and place a layer of them in your pork fat; sprinkle on a little pepper and salt; add cloves, mace, and sliced onions; if liked, lay on bits of the fried pork, and crackers soaked in cold water. Repeat this till you put in all the fish; turn on water just sufficient to cover them, and put on a heated bake pan lid. After stewing about 20 minutes, take up the fish, and mix two teaspoonfuls of flour with a little water, and stir it into the gravy, adding a little pepper and butter. A tumbler of wine, catsup, and spices will improve it. Cod and bass make the best chowder. In making clam chowder, the hard part of the clam should be cut off and rejected.
Fish glue consists almost wholly of gelatine; 100 grains of good dry isinglass, containing rather more than 98 of matter soluble in water.