A fixed oil extracted from the fresh livers of the cod, Gadus Morrhua, B.P. (or of other species of Gadus, U.S.P.), by the application of a heat not exceeding 180° F.

Characters. - Pale yellow, with a slight fishy odour, and bland fishy taste.

Test. - A drop of sulphuric acid added to a few drops of the oil on a porcelain slab develops a violet colour, which soon passes into a yellowish or brownish red.

Composition. - Contains olein (7 per cent.), palmitin (25 per cent.), and some stearin, also minute traces of iodides, and a peculiar substance probably allied to biliary acids.

Dose. - From 1 to 8 fl. dr.

Action. - Cod-liver oil is rather a food than a medicine, and its therapeutical use depends on two properties, viz. its ready absorption and its ready assimilation.

Its ready absorption is probably partly due to the presence of biliary matters in the oil, since oil passes more readily through a membrane when it is moistened with bile. If you take two loops of intestine and fill one with ordinary oil and the other with cod-liver oil, and replace them, the one with cod-liver oil will lose more in the same time than that containing ordinary oil.

It is readily assimilated, and hence it is used in all diseases where nutrition is slow, as in enlarged glands, catarrhal pneumonia, bronchitis, etc. By means of its property of stimulating nutrition, cod-liver oil improves all the functions of the body, but has no specific action on any of the organs themselves. When large quantities of the oil are taken into the stomach they cause vomiting, but if the oil be finely divided previously, it can be taken without discomfort. Hence it is advisable, when giving it in any quantity, to make it into an emulsion. Potash is sometimes used, but in the stomach the potash is probably neutralised, the emulsion decomposed, and the oil liberated. A better method is to mix it with an equal volume of mucilage of acacia and a few drops of oil of lemon; this emulsion is not decomposed by the acid of the stomach. The oil can also be mixed with isinglass and taken as jelly. Some people take it best by putting a little salt on the tongue before, and eating a piece of bread after the oil. It is often digested if taken with a little ether, for the ether stimulates the pancreatic secretion.

The oil must not be pressed if it causes nausea or diarrhoea - for it is a food and not a medicine, and must not be given if detrimental to the appetite.

It can sometimes be taken in a single dose at bed-time, when it cannot be retained during the day. It is rarely well borne when taken on an empty stomach, but is best retained when given not immediately after, but from half an hour to two hours after a meal. Probably the partially digested food then forms it into an emulsion.

Uses. - Externally, cod-liver oil is a good application for the removal of scales in seborrhoea, eczema, and psoriasis. In wasting diseases of children, when it cannot be borne by the mouth, it may be rubbed into the skin twice daily.

Internally, cod-liver oil is used in all diseases arising from defective nutrition and in all scrofulous conditions (of the skin, bones, &c), and as a food during chronic illnesses and in convalescence from acute diseases.

In children emaciated with diarrhoea, a useful mixture is vinum ferri and cod-liver oil; it must not be given in such quantities as to increase the diarrhoea. Often it will also relieve constipation in children.

Its nutritive properties are especially directed to glandular tissues; hence it is used in all cases of enlarged glands, as in tabes mesenterica.

In malnutrition of the heart, and defective circulation, it improves the condition of the heart, increases the red corpuscles, and to some extent also the white corpuscles; hence it is useful in old people with giddiness and a tendency to syncope.

It is also used in chronic rheumatism and tertiary syphilis.

It is also a tonic to the nervous system, and is of great service in cases of nervous debility consequent on hard work, worry, or acute disease. It is used in neuralgia with iron and port wine. In hysteria in middle-aged persons it is often serviceable.

In rickets it may be given alone or in combination with phosphate of calcium.

In inflammations, as bronchitis, newly developed cells are present in great abundance, but nutrition is so defective that they cannot take on the character and functions of mucous cells, and hence, in order to allow them to form a new mucous membrane, they must be supplied with a readily assimilable nutritive material; this is probably the explanation of the benefit obtained by the use of cod-liver oil in bronchitis and other diseases dependent on malnutrition.

In chronic bronchitis, with violent cough and abundant sweetish expectoration, it gives great relief.

In phthisis it is of great service, and is used in all stages of the disease except when the temperature is very high; especially is it useful in the first stage, where there is little consolidation. Under its use the patient gains flesh, keeps the disease in check, and even sometimes becomes cured.

In catarrhal conditions of other mucous membranes besides those of respiration it is very useful, as in ozaena in children recovering from measles, and in otitis after scarlet fever.