It is highly volatile, and the putrefaction of organic fluids is indefinitely postponed where its vapour is present. Carbolic acid is soluble in different degrees in water, alcohol, ether, glycerine, fixed oils, gutta percha, india-rubber, and shell-lac. Its varying affinity for these substances enables the surgeon to modify the application of carbolic acid in various ways; these modifications are necessary to fully utilise its properties. Water dissolves the crystallised acid but sparingly, 1 part in 20 being a concentrated solution, and allows it to escape readily. The aqueous solution is therefore useful where the effects of the acid are required copiously, but only temporarily. Glycerine and the fixed oils dissolve a far greater amount of the acid, and part with it unwillingly. Their solutions are adapted for the continuous but abundant application of the antiseptic. Shell-lac, and some other substances, hold the carbolic acid still more tenaciously, and are valuable as solid storehouses which yield up the antiseptic in small quantity for a considerable period.
Carbolic acid stimulates raw surfaces, and when concentrated even destroys animal tissues. It is a local anæsthetic; with moderate doses, wounds lose their sensibility after the first smarting of the application has passed off. When given in large quantities the acid produces a peculiar kind of delirium, and temporary paralysis of sense and motion: fatal results have followed its internal application.
It is rapidly absorbed into the blood from wounded surfaces, and through the skin, whence it is discharged from the body by the lungs and kidneys. The urine of patients dressed with carbolic acid, though of normal colour when passed, assumes a dark greenish-brown hue after a few hours’ exposure to the air and light.
How much of the antiseptic must float in the atmosphere to prevent fermentative changes has not yet been determined; Bucholtz found that 1 part of carbolic acid in 600 of milk almost entirely prevented lactic fermentation, while 1 in 285 did so altogether. Alcoholic fermentation in sugary fluids was arrested by a similar quantity.
When using the acid in dressing wounds, the watery solution, the solid mixture, and the oily solution are necessary. The first to neutralise the effects of exposure to the atmosphere and water before the wound is closed; the second solid mixture in the form of plaster to provide a very scanty but continuous supply of carbolic vapour close to the wound: too scanty to irritate the raw surface, yet enough to check putrifaction in the discharge oozing from it. The third, or oily solution, is to supply the carbolic vapour abundantly to the linen dressings, appointed to receive the discharge when it has passed from the vicinity of the wound. The tin is used to afford as close a cover as possible to the breach of surface; for this purpose it must be as flexible as possible that it may fit the wound exactly.
The carbolic plaster is made of 3 parts of shell-lac and 1 part of carbolic acid crystals melted together and spread on calico. To render the lac plaster non-adhesive that it may not stick to the tender wound, it is painted with solution of gutta percha, which dries and leaves a thin film of that substance covering the plaster. This film is easily removed by rubbing the surface with a rough towel should an adhesive quality be desired. In either state the carbolic acid continues to volatilise slowly when the plaster is laid over the wound.
When adopting this method of treating wounds the following materials are necessary:—
1. Aqueous solution of crystallised carbolic acid (1 part in 20).
2. Carbolic oil: 1 part of carbolic acid in 5 of olive oil.
3. Lister’s shell-lac plaster.[1]