Prep. 1. The livers, being removed from the fish, are piled on layers of fir-twigs placed in tubs perforated at the bottom, and are allowed to remain for a considerable time exposed to the sun and air. As the livers putrefy, the oil runs out and flows through the holes in the tubs into vessels placed to receive it.
2. The partially decomposed livers, cut into pieces, are heated in iron pots without water, and the oil is poured off and set aside to deposit impurities.
3. (Savory.) The livers taken from the fresh fish are carefully washed. The large veins are then divided through their whole length, and any blood in them is carefully rinsed away. The livers are now cut into pieces, again washed and drained, and afterwards placed with a small quantity of water in vessels gently heated by steam. As the heat increases, the oil separates and rises to the surface, from which it is skimmed off; and after well cooling, to allow the deposit of some of the margarin, it is repeatedly filtered through flannel bags and finally through paper. This process gives a fine, clear, straw-coloured oil, having but a slight smell and taste.
4. (Donovan.) The perfectly fresh livers are placed in a metallic vessel and heated with constant stirring to 180° Fahr., by which treatment they break down into a uniform pulpy, liquid mass. This mass is immediately transferred to calico bags, whence the oil drains out; after filtration, while still warm, this oil is sufficiently pure for use.
Obs. Three kinds of cod-liver oil are usually distinguished—the pale yellow, pale brown, and dark brown. The latter is the most impure; its odour and taste are extremely disagreeable. The most conflicting opinions have been expressed by medical men as to the relative value of the light brown and yellow varieties. Ozonised cod-liver oil is said to be prepared by passing oxygen into the oil, and then exposing it to sunlight. Dr Letheby applied the most delicate tests to this much-vaunted remedy, but was not able to detect the slightest trace of ozone.
Prop. and Uses. Cod-liver oil has acquired much reputation for its remedial powers in pulmonary consumption, scrofulous and other glandular affections, chronic gout and rheumatism, certain skin diseases, and several other ailments. It is generally supposed that the iodine and bromine, which are present in minute quantities in this fish, are the substances to which it owes its efficacy. “Dr De Jongh refers its virtues to the presence of both iodine and the elements of the bile. Our own researches lead us to infer that one of its most active constituents is free phosphorus. Good cod-liver oil contains fully ·02 of this substance, as well as about ·09 of phosphoric acid. Now, the marked action of minute doses of phosphorus on the nervous, vascular, and secreting organs, is well known to every experienced surgeon. The difficulty, however, of bringing it into a form adapted for administration has hitherto prevented phosphorus being extensively employed as a therapeutic agent. This obstacle is removed by the employment of cod-liver oil. Nature has here provided a simple remedy, which the ingenuity of man has failed to produce artificially. This opinion is borne out by the facts, that cod-liver oil cures those forms of scrofula and other diseases which do not yield to iodine, and that those varieties of the oil are the most active which contain the most free phosphorus. We, therefore, think it reasonable to conclude, that the efficacy of cod-liver oil depends on the joint action of the minute quantities of iodine, phosphorus, and the elements of the bile which it contains, and not on any one separately; and that no substance, at present known, can be used as a substitute for it.” (Cooley.)—Dose, 1 to 8 dr., in water, syrup, or orange juice; or made into an emulsion with 1 fl. oz. of peppermint water.
M. Duquesnel states that cod-liver oil flavoured with essence of eucalyptol, in the proportion of one part of the essence to a thousand, has neither the taste nor the odour of cod-liver oil. It is taken with facility, only leaving at the back of the mouth and on the tongue the taste of the essence. M. Duquesnel adds that the offensive eructations arising from cod-liver oil are completely corrected.
Cod-liver Oil Jelly. Take of cod-liver oil, 85 parts; isinglass, 3 parts; sugar, 8 parts; water, 4 parts. It forms a semi-transparent jelly of a yellowish-green colour, having a strong odour, but less strong taste of the oil. The advantages of this preparation are—its easy administration, complete retention, and assimilation by the weakest stomach. A teaspoonful is said to be equal to a tablespoonful of the ordinary oil. A lemon flavour may be imparted to it with advantage if desired.
Cod-liver Oil and Lacto-Phosphate of Lime. (Shinn.) Cod-liver oil, 1 pint; oil of bitter almonds, peppermint, and winter green, of each 10 drops; powder of gum Arabic 4 oz.; sugar, 6 oz.; solution of lacto-phosphate of lime (60 gr. to 1 fl. oz.), 61⁄2 fl. oz.; lime water, 61⁄2 fl. oz. Mix the gum and sugar in a capacious mortar, and make a smooth mucilage with the lime water and 3 oz. of the solution of lacto-phosphate of lime. Add the volatile oils to the cod-liver oil, and gradually triturate them with the mucilage, until a perfect emulsion is formed. Finally, add the rest of the solution of the lacto-phosphate of lime, and mix thoroughly. The solution of lacto-phosphate of lime is made by saturating a solution of lactic acid with freshly precipitated phosphate of lime.
Cod-liver Oil with Iodide of Iron. Triturate iodide of iron, with cod-liver oil, 4 gr. to the ounce, until dissolved. Horsley’s patent is as follows:—Dissolve 22 scruples of iodine in a gallon of cod-liver oil, at a temperature of 140° Fahr., in a water-bath. Add to the solution 8 scruples of iron (reduced by hydrogen), and heat to 180° Fahr., until the combination is complete.—Dose, 1 dr. to 1⁄2 oz.