Cod-Liver Oil, the oil drained or expressed from the livers of the cod, and also of the pollock, hake, and haddock, largely used in medicine. Other fish oils are sometimes fraudulently substituted; the adulteration is to be detected by the taste and smell, the absence of the violet or red color reaction with sulphuric acid characteristic of the biliary acids, and by the specific gravity, that of shark liver oil, which also gives the violet reaction with sulphuric acid, being 0.866, which is less than that of cod liver oil. The latter varies in color from a light yellow to a dark brown, and in taste and smell from a slight and hardly disagreeable, though characteristic flavor and odor, to a nauseous taste and a repulsive odor. These varieties depend upon the condition of the livers at the time of the extraction of the oil, and upon its subsequent treatment. That which is derived from fresh livers is the lightest in color and has the least smell. The darker and more disagreeable varieties are procured from livers which have undergone more or less putrefaction. The chemical composition of cod liver oil is not yet satisfactorily made out.
It contains a dark brown, odorless and tasteless substance called gaduine; oleine and margarine; butyric and acetic acids; biliary principles; iodine, chlorine, and bromine in exceedingly small quantities; phosphoric and sulphuric acids; phosphorus, lime, magnesia, soda, and iron. The volatile alkaloid propylamine, which imparts a peculiar odor to herring pickle, and which is probable identical with secalia obtained from ergot, may be derived from cod-liver oil by distillation with ammonia. - Cod-liver oil is employed with advantage in diseases which are characterized by impaired nutrition. It is regarded as one of the most useful remedies known in medicine. In pulmonary consumption, although not a specific, it contributes, when well borne, to the nourishment of the patient, relieves many unpleasant symptoms, and often prolongs life. Its action is probably that of an easily assimilated fat, furnishing in itself an important element of food, and assisting in the assimilation of other nutritive principles. Considerable importance has been attributed to the therapeutic action of the minute quantity of iodine and other inorganic constituents which cod-liver oil contains, and with better reason to the biliary acids and other peculiar substances that enter into its composition.
The biliary principles may probably be found in larger proportion in the "extract of cod liver," prepared by evaporating the watery liquid which escapes from the liver when the oil is extracted, than in other preparations of oil. This preparation has been declared, chiefly however by those interested in its sale, to possess a degree of remedial efficacy that has not yet been proved. The chief objection to the administration of cod-liver oil, and one that is sometimes insu-perable, is its taste. This may be more or less completely disguised by aromatics, bitters, oil of bitter almonds, or the froth of porter. It may be partially saponified by an alkali, or made into an emulsion. One of the simplest and easiest methods of avoiding its disagreeable taste is to masticate a few cloves and swallow the oil before their pungent impres- sion upon the mouth has departed, when the taste of the oil will not be perceived. Cod-liver oil is chiefly used as a remedy in pulmonary consumption, but its efficacy is not confined to this affection. It may be advantageously prescribed in many forms of impaired nutrition, and especially in the protean derangements resulting from impaired nervous power. It should not be administered when it reduces the appetite or disturbs digestion.
It is usually borne best if it is taken about an hour after a meal. Its good effects are most evident when it has been taken for several months consecutively. The dose is from a teaspoonful to a tablespoonful three times a day. Four or five grains of pancreatine added to each tablespoonful will make the oil set better.