Carbolic acid liquefied by the addition of 10 per cent. of water.

Characters. - A colourless or very slightly reddish or brownish liquid having the taste, odour, etc, of carbolic acid.

Solubility. - It dissolves in 18 to 26 per cent. of water at 60° F. (15.5° C), yielding a clear or nearly clear solution, from which any slight coloured impurity contained previously in the acid separates as dark oily drops.

Dose. - 1 to 4 minims.

Action. - Carbolic acid is a powerful deodoriser and disinfectant (p. 106). It precipitates albumen, and destroys low organisms. It prevents the decomposition of albuminous fluids by bacteria, and the fermentation of sugar by yeast. Quantities smaller than those which are sufficient to kill these organisms suffice to prevent their development. It does not appear to destroy the action of all organic ferments so readily, although it does so when applied for a long time, or in concentrated solution; it prevents the conversion of starch into sugar, the conversion of albumen into peptones, and the decomposition of amygdalin with formation of hydrocyanic acid. When applied to the skin it produces a white stain, and greatly diminishes the sensibility of the part. The stain afterwards becomes brownish, and of a parchment-like consistence, and the epidermis by-and-by peels off. Carbolic acid does not act as a vesicant, but appears to cause anaesthesia of the part to which it is applied, extending to some distance below the surface. If applied over a large surface of skin it may be absorbed to such a degree as to cause poisoning, and even death. The symptoms are weakness, delirium, and collapse. When applied to mucous membranes it has a similar action. In the mouth it causes a burning pain, and when swallowed produces symptoms of gastro-enteritis, pain in the stomach, and sometimes vomiting and purging. Along with this there is great collapse, delirium, and death, sometimes, though not always, preceded by convulsions, the pupils being contracted. After death the blood is found to be very dark, and its coagulability greatly diminished. Carbolic acid appears to be a powerful poison to all the tissues, paralysing both muscle and nerve when applied directly to them without previously stimulating them. After absorption it acts especially on the medulla oblongata, but acts also on the spinal cord, first stimulating and then paralysing these centres. From its action on the cord it produces in frogs convulsions resembling those of strychnine, these being followed by paralysis. It first stimulates the respiratory and vaso-motor centres, and afterwards paralyses them. It thus produces at first quickened respiration with rise of blood-pressure, and it also quickens the pulse. As the centres become paralysed the blood-pressure falls greatly, the respiration becomes slower, and the pulse also becomes slower. When it is injected directly into the blood, so that it can act in large quantity on the nerve-centres, it paralyses the vaso-motor centre at once, and causes the blood-pressure to fall very greatly without much alteration being observed in the action of the heart itself. That the vaso-motor centre is completely paralysed by carbolic acid is shown by the fact that after its injection the blood-pressure is not raised either by stimulation of sensory nerves or by asphyxia. Although carbolic acid acts first and most markedly on the nerve-centres in the medulla oblongata it affects the cerebral centres also. This effect is evidenced in man by headache, giddiness, and lassitude, followed by unconsciousness. In animals it also affects the cerebrum, as shown by alterations in sensibility and motor power. It stimulates the sweat centre and salivary centres, producing perspiration and salivation. Medium doses appear to cause death by paralysis of the respiration, so that artificial respiration may be of some use in preventing it; but large doses paralyse the heart also, so that death occurs in spite of artificial respiration. It diminishes the temperature in cases of poisoning, and also when given to animals in a febrile condition, though when the fever is very high it does not seem to have much effect. It is excreted by the kidneys, and can be readily detected in the urine by bromine water. It sometimes gives rise to a very dark colouration of the urine, due to some oxidation-product of the carbolic acid, probably hydroquinone (p. 809).

Part of the carbolic acid appears in the urine, in combination with sulphuric acid, as sulpho-carbolates, and if the quantity administered has been large the ordinary sulphates may completely disappear. The hydroquinone occurs also to a great extent in the urine in combination with sulphuric acid. The compound is colourless, and thus the urine, when freshly passed, has a normal appearance; on standing, the hydroquinone becomes free, undergoes further oxidation, and causes the urine to assume a brown colour.

Treatment of Poisoning. - The stomach should be emptied by emetics, or best by the stomach-pump. Demulcents, such as olive oil, should then be administered. For the treatment of the general symptoms following carbolic acid poisoning, and to aid the elimination in the urine, the administration of sulphates - e.g. sodium sulphate in 10-grain doses - is advisable.

Uses. - It has sometimes been applied externally to produce local anaesthesia for slight operations, such as opening abscesses.

When mixed with oil, in the proportion of ten minims to an ounce of oil, it relieves the pain of burns. One of the best means for removing the pain of toothache is to dip a little cotton-wool into carbolic acid melted by the aid of heat, and insert the pledget into the cavity of the tooth, covering it over with dry cotton-wool, to prevent the tongue being burned by contact with the acid. It is used as a stimulant to indolent ulcers and wounds, and to destroy condylomata, and has been applied to the throat in cases of diphtheria, ulceration, and aphthae. It has been employed as an injection in deep-seated inflammations such as chronic synovitis, inflamed glands, boils, hydrocele, erysipelas, and poisoned wounds. Carbolic acid, 2 per cent. in simple ointment, is useful in relieving itching in chronic eczema and urticaria, and in papular eczema it gives relief when applied in a lotion of one part of the acid to one part of boric acid and 200 parts of alcohol. It is used locally as an antiparasitic in favus, tinea versicolor, and ringworm. Its chief application, however, is to destroy the minute organisms which cause putrefaction in albuminous fluids, and to prevent the untoward results which would arise from the absorption of putrid discharges.

According to Sir Joseph Lister, the untoward consequences of operations are frequently due, not to the operation itself, but to the poisoning of the wound by the products of decomposing discharges, and poisoning of the system generally by absorption of these products. The decomposition is due to low organisms, such as bacteria, introduced from without, and it may be prevented by the use of such substances as will prevent their development or destroy them when present. In performing operations, therefore, he advises that the skin should first be washed with a watery solution of carbolic acid (1 in 40), that the instruments also should be treated with a similar solution, and that the incision should be made under a spray of carbolic acid (1 in 60).1 After the operation is concluded under a constant use of the spray, the wound is covered with a protective consisting of varnished linen dipped in a solution of carbolic acid (1 in 40), above which are laid eight layers of gauze, steeped in a mixture of carbolic acid (1), resin (4), and paraffin (4). Between the sixth and seventh layers is put a piece of waterproof tissue, in order to distribute the discharge and prevent it from oozing out at one spot. If the discharge be great the dressings ought to be changed once in twenty-four hours, under the spray; but as the wound heals, the intervals between the dressings may be lengthened.

A solution of carbolic acid in oil is frequently used to lubricate, and at the same time disinfect, catheters (p. 105); but, as Koch's experiments show, such a solution has no antiseptic power, and they ought to be first disinfected with an aqueous solution and afterwards oiled.

Carbolic acid is very useful in what is sometimes known as an influenza cold, beginning with coryza, spreading down the throat to the air-passages, leading to severe bronchitis with much depression, and occasionally also to gastro-intestinal catarrh. This form of cold appears, like true influenza, to be extremely infectious, and to be easily communicated, not only by one member of a family to another, but even by casual visitors. It may sometimes be arrested, and may frequently be rendered less severe, by carbolic acid spray applied to the nostrils and by the use of a gargle containing carbolic acid. Other forms of sore-throat are also relieved by gargles containing about 1 per cent. of carbolic acid. Considerable care must be taken in using the gargle not to swallow it, on account of the poisonous properties of the acid. When the cold begins in the nose the solution of carbolic acid for spray may contain 1 per cent., but perhaps a still better method of applying it is by a small ear-syringe, as a 1/4 or 1/2 per cent. solution. A mixture of 1 part of carbolic acid with 3 of creasote has been used for continuous inhalation in phthisis by means of the oro-nasal respirator.

Carbolic acid is also used as an injection to wash out serous cavities, after the evacuation of fluids; for example, the cavity of the pleura after the evacuation of the fluid in pleurisy, and the cavity of an abscess after the removal of the pus. Internally, the acid has been given in cases of flatulent dyspepsia. It is a useful application to the uterus in chronic inflammation, excoriation, catarrh, and cancer, and as an injection in leucorrhoea.

1 The strength of solution placed in the bottle of the spray-producer is 1 in 20, but when mixed with the steam it is reduced to 1 in 60.

Sodii Sulpho-carbolas, B. and U.S.P. Vide p. 626.

B.P. Zinci Sulpho-carbolas. Vide p. 671.