This section is from the book "Materia Medica Pharmacy, Pharmacology And Therapeutics", by W. Hale White. Also available from Amazon: Materia Medica Pharmacy, Pharmacology And Therapeutics..
A fixed oil obtained from fresh livers of Gadus Morrhua Linne, and of other species of Gadus (class Pisces: order Teleostia; family Gadida.)
North Atlantic Ocean. An oil obtained from the Candle fish ( Thaleichthys Pacificus) is found in the markets under the name of Eulachon Oil and is sometimes sold as Cod Liver Oil.
The fresh livers are slowly heated, and the oil is decanted from the water, and sometimes deprived of the solid fat by partial freezing.
A pale yellow, thin, oily liquid, having a peculiar, slightly fishy, but not rancid odor, and a bland, slightly fishy taste. Sp. gr., 0.920 to 0.925.
The chief constituents are - (1) Olein, 70 per cent., which is a fluid fixed oil, and is Glycerin Oleate the most abundant constituent of Cod Liver Oil. (2) Palmilin, with some Stearin, 25 per cent. (3) Free fatty acids, as Oleic, Palmitic, Stearic. (4) Gaduin, C35H46O9, a peculiar principle, very insoluble in ordinary menstrua. (5) Morrhuol, a crystalline substance of uncertain composition, containing Phosphorus, Iodine and Bromine. (6) Traces of Iodine and Bromine. (7) Biliary principles. The so-called alkaloids of Cod Liver Oil are decomposition products, ptomaines or cadaveric alkaloids, and are found in larger quantities in the brown oils. Their existence in fresh oil obtained from healthy livers has not been demonstrated. Dose, 1 to 4 fl. dr.; 4. to 15. c.c.
Cod liver oil is a bland unirritating oil. If it is desired to administer it in cases in which it is rejected by the stomach, it may be rubbed into the skin. The oil is certainly absorbed when applied in this way.
Gastro-intestinal tract. - Cod liver oil, even more than other oils, is liable to cause indigestion, nausea, and sickness. Large doses may set up diarrhoea. It is more readily absorbed than other oils. Loops of intestine have been isolated in the lower animals, and into each loop different oils have been injected. The intestines are returned to the abdominal cavity, and after some time the animal is killed and the loops are opened. It is always found that the cod liver oil has been more rapidly absorbed than any other oil. The facility with which cod liver oil is absorbed is also shown by the fact that it often cannot be recognized in the faeces, although equal quantities of other oils taken by the mouth are passed unaltered. Some authorities believe that the superior absorbability of cod liver oil depends on the biliary principles contained in it, but this is doubtful; others think that it is because the presence of free acids facilitates saponification and emulsion. Certainly it contains more free fatty acids than other oils, and it also emulsifies much more easily.
Tissues. - Not only is cod liver oil more readily absorbed than other oils, but it is a better food. All oils lead to an increased formation of fat, but cod liver oil is the most powerful in this respect. It reduces the color of a solution of potassium permanganate more readily than other oils - that is to say, it is more readily oxidized. Thus, as it is more easily absorbed and more easily oxidized, we have a partial explanation of its peculiar value in increasing the weight of the body; but the general belief is that these two facts do not wholly explain the action of cod liver oil, and that it has some peculiar specific action not yet understood, especially upon those suffering from phthisis for whom it is a very valuable drug. If it is true, as has been stated, that iodine may occur in the proportion of 1 to 2000 of the oil, the influence of this remedy is not to be ignored.