Cod-liver oil contains palmitin, stearin and other more complex glycerides; the "stearine" mentioned above, however, contains very little palmitin and stearin. Several other acids have been identified: P. M. Meyerdahl obtained 4% of palmitic acid, 20% of jecoleic acid, C19H36O2, and 20% of therapic acid, C17H26O2; other investigators have recognized jecoric acid, C18H30O2, asellic acid, C17H32O2, and physetoleic acid, C16H30O2, but some uncertainty attends these last three acids. Therapic and jecoleic acids apparently do not occur elsewhere in the animal kingdom, and it is probable that the therapeutic properties of the oil are associated with the presence of these acids, and not with the small amount of iodine present as was at one time supposed. Other constituents are cholesterol (0.46-1.32%), traces of calcium, magnesium, sodium, chlorine and bromine, and various aliphatic amines which are really secondary products, being formed by the decomposition of the cellular tissue.
Cod-liver oil is used externally in medicine when its internal administration is rendered impossible by idiosyncrasy or the state of the patient's digestion. The oil is very readily absorbed from the skin and exerts all its therapeutic actions when thus exhibited. This method is often resorted to in the case of infants or young children suffering from abdominal or other forms of tuberculosis. Its only objection is the odour which the patient exhales. When taken by the mouth, cod-liver oil shares with other liver-oils the property of ready absorption. It often causes unpleasant symptoms, which must always be dealt with and not disregarded, more harm than good being done if this course is not followed. Fortunately a tolerance is soon established in the majority of cases. It has been experimentally proved that this is more readily absorbed than any other oil--including other liver-oils. Much attention has been paid to the explanation of this fact, since knowledge on this point might enable an artificial product, without the disadvantages of this oil, to be substituted for it. Very good results have been obtained from a preparation named "lipanin," which consists of six parts of oleic acid and ninety-four of pure olein. Cod-liver oil has the further peculiarity of being more readily oxidizable than any other oil; an obviously valuable property when it is remembered that the entire food-value of oils depends on their oxidation.