1911 Encyclopædia Britannica/Cod-liver Oil
COD-LIVER OIL (Oleum Morrhuae, or Oleum Jecoris Aselli), the oil obtained from the liver of the common cod (Gadus morrhua). In the early process for extracting the oil the livers were allowed to putrefy in wooden tubs, when oils of two qualities, one called “pale oil,” and the other “light brown oil,” successively rose to the surface and were drawn off. A third oil was obtained by heating the liver-residues to above the boiling-point of water, whereupon a black product, technically called “brown oil,” separated. The modern practice consists in heating the perfectly fresh, cleaned livers by steam to a temperature above that of boiling water, or, in more recent practice, to a lower temperature, the livers being kept as far as possible from contact with air. The oils so obtained are termed “steamed-liver oils.” The “pale” and “light brown” oils are used in pharmacy; the “brown” oil, the cod oil of commerce, being obtained from putrid and decomposing livers, has an objectionable taste and odour and is largely employed by tanners. By boiling the livers at a somewhat high temperature, “unracked” cod oil is obtained, containing a considerable quantity of “stearine”; this fat, which separates on cooling, is sold as “fish stearine” for soap-making, or as “fish-tallow” for currying. The oil when freed from the stearine is known as “racked oil.” “Coast cod oil” is the commercial name for the oil obtained from the livers of various kinds of fish, e.g. hake, ling, haddock, &c. The most important centres of the cod-liver oil industry are Lofoten and Romsdal in Norway; the oil is also prepared in the United States, Canada, Newfoundland, Iceland and Russia; and at one time a considerable quantity was prepared in the Shetland Islands and along the east coast of Scotland.
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.
Cod-liver oil may be given in all wasting diseases, and is occasionally valuable in cases of chronic rheumatoid arthritis; but its great therapeutic value is in cases of tuberculosis of whatever kind, and notably in pulmonary tuberculosis or consumption. Its reputation in this is quite inexpugnable. It is essential to remember that “in phthisis the key of the situation is the state of the alimentary tract,” and the utmost care must be taken to obviate the nausea, loss of appetite and diarrhoea, only too easily induced by this oil. It is best to begin with only one dose in the twenty-four hours, to be taken just before going to sleep, so that the patient is saved its unpleasant “repetition” from an unaccustomed stomach. In general, it is therefore wise to order a double dose at bedtime. The oil may be given in capsules, or in the form of an emulsion, with or without malt-extract, or success may be obtained by adding, to every two drachms of the oil, ten minims of pure ether and a drop of peppermint oil. The usual dose, at starting, is one or two drachms, but the oil should be given eventually in the largest quantities that the patient can tolerate.