Salicis Cortex-Willow Bark. (Not Officinal.) -The bark of Salix caprea. and other species.

Characters.-Quilled pieces, the epidermis dark, the structure fibrous and tough ; odour slightly aromatic; taste bitter and astringent.

Composition.-Willow bark contains salicin, tannic acid, and the ordinary constituents of barks.

Non-officinal Preparations.

1. Salicinum

Salicinum. Salicin, C13H1807. A neutral principle in silky acicular crystals, or white tables; odourless, bitter. Solubility, 1 in 20 of water. Dose, 5 to 30 gr.

2. Acidum Salicylicum, C7H603, or H1.C7H403. Source.Prepared from the oil of Gaultheria procumbens (Winter Green), or commercially by passing a stream of Carbonic Acid over a heated mixture of Carbolic Acid and Caustic Soda, decomposing by Hydrochloric Acid, and purifying.

Characters.-Light acicular crystals; odourless, but irritant to the nostrils; with a sweetish taste. Solubility,

1 in 760 water; 1 in 4 of spirit.

Dose.-5 to 30 gr. or more.

From Acidum Salicylicum is prepared:

Sodae Salicylas, Na2.C7H403. Source.-Made by neutralising the Acid by Bicarbonate of Soda in water; or as the acid without the final decomposition.

Characters.-Shining silky tabular crystals, or a white crystalline powder, odourless, with a sweetish unpleasant taste. Solubility, 1 in 1 of water.

Dose.-10 to 30 gr.

Action And Uses. 1. Immediate Local Action And Uses

Externally.-Salicylic acid acta as an antiseptic and disinfectant, not inferior to carbolic acid. At the same time it stimulates the local circulation. It is extensively used as a surgical dressing in the form of cotton wool impregnated with the acid by the aid of glycerine. On the contrary, salicylate of soda has no antiseptic or disinfectant power, unless combined with a mineral acid to liberate the salicylic acid. Salicylic acid in powder, diluted with talc, is a anhidrotic, checking local perspirations of the feet, or the general perspirations of phthisis. Neither substance is absorbed by the unbroken skin.

Internally.-Salicylic acid causes sneezing and cough when applied to the nose, or inhaled, like benzoic acid; and when admitted to the stomach, it is also a local irritant, causing heat, pain, nausea, and vomiting, unless in moderate and well-diluted doses. The soda salicylate is very much less irritant, and may be freely administered if pure. The latter drug is used for sarcinous vomiting, and in some cases of chronic dyspepsia with decomposition. Salicin is easily borne by the stomach. In the bowel it is converted into saligenin (C7H802) and glucose; and the former is in turn broken up into salicyluric (HC9H8N04), salicylic, and salicylous acids (C7H602). Salicylous acid is a local irritant.

2. Action On The Blood And Its Uses

Salicylic acid necessarily exists in the blood as the salicylate of soda, being taken up with considerable rapidity. The acid is possibly again liberated in part by the free carbonic acid of the plasma in inflamed parts of the body, and thus exerts its antiseptic action within the body; but this is doubtful. Either in the blood, or in some of the tissues, a portion unites with glycocoll (just like benzoic acid), and forms salicyluric acid (comparably with hippuric acid), thus: C7H603 + C2H5NO2 (glycocoll) = H.C9H8N04 (salicyluric acid) + H10.

As regards salicin, the decomposition begun in the bowel is continued in the blood.

3. Specific Action And Uses

The action of salicylic acid and its sodium salt is identical in the tissues, since the former is converted into the latter. A moderate dose causes increased cardiac action, flushing and warmth of the surface, perspiration, a full feeling in the head, tinnitus, deafness, impairment of vision, and possibly a slight fall of temperature, although the nitrogenous waste is said to be increased. Larger doses may cause delirium. Respiration is temporarily disturbed; the heart is depressed after the primary excitation; the vessels are relaxed, and the blood pressure falls; perspiration is increased; the peripheral nerves, both sensory and motor, are unaffected.

All these phenomena in the healthy subject, taken together, do not account for the remarkable effect of salicylates upon the body temperature in pyrexia or fever. Of all antipyretics these appear to be the most powerful, two or more moderate doses (15 to 20 gr.) within one or two hours reducing pyrexial temperatures several degrees, according to the disease and the subject. It is therefore probable that the salicylates act upon some pathological cause of pyrexia, possibly the organisms of the specific fevers.

Salicylate of soda is employed in two allied but distinct classes of cases: 1. In pyrexia from any cause, such as typhoid fever, pneumonia, pyaemia, etc., it is a simple and powerful antipyretic. In this respect it is comparable with quinia; only more rapid in its action, less lasting in its effects, and more depressant to the circulation. It may be given in these diseases in single full doses when the temperature exceeds a certain height, say 104° Fahr. 2. In acute rheumatism, salicylate of soda is distinctly a specific (much as quinia is a specific against malaria), reducing the temperature, relieving the pain, removing the swelling and other local symptoms, and shortening the duration of the disease. By thus curtailing the course of rheumatism, this drug may indirectly reduce the liability to cardiac and other complications; but it is of no great service directly in this respect. It is of no use in chronic rheumatism or in gout; of doubtful value in rheumatic sciatica. It may be given either in wafers or in solution; and in this country it is now often combined with bicarbonate of potash in free doses (20 gr.). When the pyrexia declines, the dose of the salicylate must be most gradually reduced, as relapses are extremely common after it has been discontinued.

Diphtheria and diabetes have sometimes been successfully treated with salicylates.

Salicin may be used for the same purposes as the salicylates; its action, if less powerful, being better sustained, and the cardiac and vascular depression less marked.

4. Remote Local Action And Uses

Salicylic acid is slowly excreted in the urine, sweat, saliva, bile, and mucous secretions generally, mostly as the salicylate or the free acid, partly as salicyluric acid.

Its most important action remotely is on the kidneys and urinary passages, where it is a stimulant and disinfectant, at the same time increasing the acidity. It is thus adapted for the treatment of chronic inflammatory affections of the bladder, with foul alkaline urine and phosphatic deposits. Sometimes, however, it so irritates the kidney as to cause albuminuria and even haematuria; and it must be used with great caution, for these or other purposes, if renal disease be present.