The oil extracted by a steam heat not exceeding 180° from the fresh liver of the Cod (Gadus Morrhua) and others of the Family GadidAe, as the Dorse (Gadus callarias), the Pollack (Gadus pollachius), the Coal Fish (Gadus carbonarius), the Whiting (Gadus merlangus), and the Ling (Gadus molva).
History. Cod Liver Oil has, for a long period, been esteemed in Germany and Holland, in the treatment of scrofulous and rheumatic diseases. It was introduced into England by Dr. Percival, in 1771, as a remedy for Chronic Rheumatism, and was employed in the Manchester Infirmary some time after this period. It, however, fell into disuse till Schenk published an account of sixteen cases of Chronic Rheumatism successfully treated by it. It was not, however, till 1841 that its value was fully understood by British practitioners, when Dr. J. H. Bennett published an Essay on its properties; since that date it has been fully recognised as a remedy of great power and usefulness in tubercular disease. I may add here, that the oil obtained by boiling from the liver of the Hammerheaded Shark (ZygAena. vulgaris) is amongst the native remedies of the Burmese of the Tenasserim Provinces; and I am informed by a respectable priest, that it is advised in some of their most ancient medical writings.} The only purpose that I could ascertain for which it was used was to cause the removal of opacity of the cornea; for this purpose they give it internally in large doses.
1S10. Its Chemical Composition is thus stated by Dr. Garrod:§ - " Cod Liver Oil contains Oleine, Margarine, various biliary principles, as the organic acids and colouring matter of bile; also Phosphoric and Sulphuric Acid, with salts of Lime, Magnesia, andiron; a peculiar substance, Gaduin (C35O23H9), very insoluble in ordinary menstrua, but soluble in Sulphuric Acid, and giving a blood red colour to the solution; also Iodine and Bromine. The Oleine and Margarine of this Oil are said by some to differ from that usually met with, inasmuch as no Glycerine can be obtained by their saponification, but they yield instead a peculiar body called Propylene, or Oxide of Propyl. The proportion of Iodine is not more than 05 per cent." The test for the purity of Cod Liver Oil is Oil of Vitriol If a little of the Oil be poured on a plate, and a drop of Sulphuric Acid be added, a beautiful lake or crimson colour is produced, spreading from the point of contact with the acid. This is supposed to be due to the action of the acid on the biliary principles contained in the oil.* Pereira states that "Oil of Vitriol is a test for liver oils generally. It does not distinguish one liver oil from another, for it reacts equally with the oil of the liver of the ray, and with oil of the liver of the common cod. Neither does it distinguish good Cod Liver Oil from bad, for it produces its characteristic reaction both with common brown Cod-oil and with the finest and palest qualities. But it serves to distinguish oil procured from the liver, from oil obtained from other parts of the animal '' Iodine or Iodide of Potassium may be added to Train Oil to imitate Cod Liver Oil This may be detected by shaking the suspected oil with Alcohol, which abstracts the Iodine, or by adding a solution of Starch with a few drops of Sulphuric Acid, by which the blue Iodide of Starch is produced,
* Diseases of the Heart, 3rd Ed. Treatise on Oleum Jecoris Aselli, Lend. 1841. Zevocat, their great medical authority, is supposed to have been contemporary with King David.
§ Essentials of Mat. Med. and Therap., p. 330.
There are three varieties of Cod Liver Oil met with in commerce - 1, the pale; 2, the light brown; and 3, the dark brown. The differences of colour, odour, and flavour in the varieties of Cod Liver Oil depend upon the different methods in which it is prepared, the degree of heat employed, the state of freshness or putrefaction of the livers, the quantity of decomposed matter present in the Oil, and the length of exposure to the air. The oil contained in the cells of the fresh liver is nearly colourless, and the finest specimens are nearly devoid of colour, odour, and flavour, having only a bland, fish-like, and not disagreeable taste. The dark varieties contain more empyreumatic matter and are intensely disagreeable. On the question of the relative value of the different varieties of Cod Liver Oil, the Editors of the edition of Pereira of 1857 remark: - " Experience fully confirms the inference drawn from observation of the chemical constitution of these varieties of Cod Liver Oil, as to their relative therapeutical value. At the Brompton Hospital it has been found that the use of the darker kinds cannot be long continued; the clear and straw coloured inodorous oil is that which is now administered in this institution. Dr. Williams, in the Litest edition of his Principles of Medicine, affirms the superiority of the pure fresh oil."§ Dr. De Jongh, however, advocates the use of the darker varieties, on the ground that they contain more volatile acids (butyric and acetic) and biliary matters. It is curious, however, that his analysis of the light brown oil which he recommends, contains no mention of butyric and acetic acids. Moreover, considerable doubt has been thrown on the value of bis chemical investigation || The whole experience of English practice is in favour of the pale oil Dr. Garrod sums up the arguments in its favoir thus: - " 1. It is the real oil as contained in the liver of the cod-fish, rich in biliary matters, and also in Iodine and other inorganic principles. 2. It contains no products of putrefaction, such as are found in the dark oils. 3. It sits more easily on delicate stomachs. 4. Experience has proved it to be a most effective therapeutic agent. "¶ The pale variety is officinal in the British Pharmacopoeia. Its sp. gr. is from 917 to 920.