Isinglass. [Ichthyocolla. Isinglass. U. S.] Appendix B. The swimming bladder or sound of various species of Acipenser, prepared and cut into fine shreds.

Description. Isinglass is the dried swimming bladder of the sturgeon, but many fish yield a similar substance.

Prop. & Comp. Isinglass consists of a gelatinous tissue, which, by boiling, yields gelatine, a substance which is soluble in hot water, and forms a jelly on cooling: it is precipitated by tannic, but not by gallic acid. The combination of gelatine with tannin forms the basis of leather, called often tanno-gelatine.

Off. Prep. Solution of Gelatine. [Not officinal in U. S. P.] (Isinglass, in shreds, fifty grains; warm distilled water, one fluid ounce. Mix and digest for half an hour on a water bath, with repeated shaking, and filter through clean tow, moistened with distilled water.)

Use. The solution of gelatine is introduced into the appendix of the Pharmacopoeia for separatiug tannin from gallic acid.

Oleum Morrhuae. Cod-Liver Oil. The oil extracted from the fresh liver of Gadus Morrhua by a steam heat not exceeding 180°. [The fixed oil obtained from the liver of Gadus Morrhua and other species of Gadus. U. S.]

Description. The liver of the common cod-fish and other species of gadus, frequenting the seas of northern Europe and America, yields the cod-liver oil of commerce.

The most important species of the oil yielding fish, in a medical point of view, have been thus classified: -

Gadus morrhua, or Asellus major, the common Cod-fish; found in large quantities on the coasts of England, France, Iceland, and Norway, but especially off Newfoundland.

Gadus callarias, or Asellus striatus, the Dorse; found largely on the Norwegian coast, and principally near the Lofoden Islands.

Gadus molva, or Asellus longus, the Ling; found also on the coast of Norway, though less abundantly than the above two species. Plentiful near England.

Gadus carbonarius, or Asellus niger, the Coal-fish; inhabiting the same localities as the last.

Gadus pollachius, or the Pollack; found in Norway, especially near Tromsoe.

Gadus merlangus, or Asellus albus, the Whiting; inhabiting the coasts of France. Besides many other species of less importance.

The oil may be extracted from the livers by three different methods: - by exposing them to the sun to undergo a process of fermentation; by boiling them in water for some time; or by dividing the livers, and permitting the oil slowly to drain from them.

1. The oil is sometimes obtained by packing the livers in tall vats, furnished with three taps placed at different heights, and then exposed to the sun, to favour the separation of the oil. On opening the upper tap a pale oil is obtained; from the middle one a light brown oil; and a darker brown, yet transparent, oil from the inferior. The remaining mass of livers yields, by pressure and heat, a very dark and thick product, not fit for medicinal use, but employed by curriers, etc.

2. The second method of preparing the oil is by boiling the livers in water, and afterwards separating the oil from the surface, and filtering from any albumen or cellular tissue mixed with it.

3. The following is the method now employed in the preparation of the best English cod-liver oil at Messrs. Bell and Co.'s establishment. The livers are collected daily, so that no trace of decomposition may have occurred, carefully examined, in order to remove all traces of blood and impurity, and to separate any inferior livers; they are then sliced, and exposed to a temperature not exceeding 180° Fah., till all the oil has drained from them. This is filtered; afterwards exposed to a temperature of about 50° Fah., in order to congeal much of the solid fat (margarine), and again filtered and put into bottles well secured from the action of the air.

Three chief varieties of cod-liver oil occur in commerce, distinguished by their colour: the pale is that rendered officinal, prepared in England or elsewhere; besides which there are the light brown and the dark brown oil, from Norway, etc.

The difference in colour in the different oils depends upon the circumstances attending their preparation, as the amount of heat employed, the state of freshness or putridity of the livers, the quantity of decomposed matter present in the oil, and the length of exposure to the atmosphere, etc.

Prop. & Comp. The pale oil is almost colourless when first prepared, with a slight fishy but not disagreeable odour, sp. gr. from .917 to .920, with a bland fish-like taste. The composition of the three varieties is essentially the same, but the darker contains more empyreumatic matter, and is much less agreeable to the taste. Cod-liver oil contains oleine, margarine, various biliary principles, as the organic acids and colouring matter of bile; also phosphoric and sulphuric acid, with salts of lime, magnesia, and iron; a peculiar substance, gaduin (C35 O23 H9), very insoluble in ordinary menstrua, but soluble in sulphuric acid, and giving a blood-red colour to the solution; also iodine and bromine. The oleine and margarine of this oil are said by some to differ from that usually met with, inasmuch as no glycerine can be obtained by their saponification, but they yield instead a peculiar body, called propyline, or oxide of propyl. The proportion of iodine is not more than .05 per cent. When pure cod-liver oil, spread in a thin layer on a plate, has a drop of oil of vitriol added to it, a beautiful lake or crimson colour is produced, rising from the point of contact of the oil and acid, and rapidly spreading over the surface. This is probably due to the action of the acid on the biliary principles present in the oil.

Therapeutics. Cod-liver oil is a remedy which, at the present time, stands in very high estimation, nor does it appear probable that its repute will be ephemeral in character; how it acts is yet undetermined. When taken for a time by patients who have become emaciated from any cause, and whose blood is impoverished, it frequently restores the flesh; and, from Dr. Theophilus Thomson's statements, it appears also to improve the richness of the blood. Under its influence, patients often gain an almost incredible increase of weight, exceeding many times the amount of the oil which has been taken during the period. The oil also seems to possess the power of arresting the progress of certain morbid actions, such as occur in phthisis and scrofula, and in the low form of rheumatic and other inflammations; in fact, many anomalous diseased conditions become ameliorated under its influence. It has been supposed that the iodine and bromine contained in it might produce the beneficial results, but the idea is not tenable, for the effects of these remedies are very different in character; it would seem probable that it acts simply as an oil, and that it is superior to other oils on account of its being more readily assimilated. If the statement of Winkler prove correct - namely, that the oleine differs from ordinary oleine in not yielding glycerine - this may in part explain its value. It very seldom happens that patients cannot take the remedy, even when ordinary fatty substances disagree with their stomachs; it very rarely purges, except in cases where ulceration of the intestines is present. Cod-liver oil is employed extensively in the treatment of the different stages of phthisis, and various forms of scrofula: in chronic rheumatism and neuralgia; in chronic skin affections, and many other diseases of a low type and accompanied by a cachectic condition of habit. It has been applied externally in some skin affections, and occasionally with the idea of producing by this means its constitutional effects.

Dose. From 1 fl. dim to 1/2 fl. oz.; taken on the top of water, milk, orange, wine, ale, or porter. Some patients prefer it at the time of a meal, or immediately after food.

Adulteration. Many oils may be mixed with cod-liver oil. The addition of the liver oil from other fish is not, perhaps, very important in a therapeutic point of view, and would be difficult or impossible to detect, as all give the test with sulphuric acid. When other oils, not of hepatic origin, are present, the sulphuric acid test is valuable, for the impure specimen either does not give the beautiful lake colour, or this becomes immediately mixed with, and obscured by, a dark brown substance, from the charring of the oil: such is the case with whale or seal oil; also with olive and other vegetable oils.