That counterirritation may act in other ways is also possible, for it is well known to every one that pain in a sensitive place results in a diminished sense of pain in a less sensitive region. It is probable, also, that the psychic suggestive effect, as of a thermocautery, may at times be important, and that in the treatment of muscular or other tissues in direct contact with the skin changes in the local blood-supply may account for the remedial effect. In this connection it is of interest that Lazarus-Barlow has shown that a muscle on the same side as a blister has a higher specific gravity than the corresponding muscle on the unblistered side. And Wechsberg has demonstrated that when abscesses were experimentally produced in rabbit's legs, they were less extensive and healed more rapidly on the side to which counter-irritants were applied. Oliver found that a mustard paste over the liver sent the blood-pressure from 105 to 135, and Roth, that a large hot application to chest and abdomen sent up the pressure about 8 mm. in each of two cases. But Wood and Weisman (1912) find that irritation of the skin of the hand by a mustard-bath just short of producing dermatitis does not materially increase the rate of blood-flow in the hand, the skin redness being presumably not accompanied by a change in the caliber of the deep-lying arterioles.

We may sum up, then, by repeating that the good effects of counterirritation may be due to: (1) A segmental or regional nervous relation between superficial tissues and the viscera. (2) The countering effect of a superficial pain over a deep-seated one. (3) A direct circulatory effect. (4) A psychic effect.

Counterirritant Measures

The more commonly employed counterirritant measures are: heat, cold, dry-cupping, and drugs.

Heat is applied as an electric pad, a hot-water bottle, a hot stone or flat-iron wrapped in cloth, or a poultice when the desire is to apply something that will keep hot a long time, or for a short time by an electric lamp or the high-frequency current. For a sudden application of extreme heat the thermocautery or the stupe may be employed. A stupe is a towel wrung out of very hot water; a turpentine stupe is made by sprinkling 15 or 20 minims of oil of turpentine on the hot towel. In the use of the thermocautery for counterirritant effect the skin should not be seared, but merely reddened by the rapid passage over it of the red-hot iron or platinum point. Poultices may be made of linseed meal, bread, flour, bran, or hops boiled with water and wrapped in cheese-cloth or any thin fabric. The clay poultice (cata-plasma kaolini, U. S. P., 1900), a proprietary name for which is "antiphlogistine," has kaolin and glycerin as its basis, with added small amounts of boric acid, oil of peppermint, methyl salicylate, and thymol. It has practically no absorption power for water, but acts largely by its heat (Roth); so for use it is heated in its container and smeared over the part with a knife or stick. Roth (1905) showed that it had less power as a counter-irritant and retained heat for a shorter time than a flaxseed poultice.

Cold is for the most part secured by an ice-bag or ice-water coil. It has been ascertained that locally applied heat or cold does not affect the temperature of the viscera to any extent, and that their value in internal inflammations is not antiphlogistic but reflex. Cold is often applied directly to an injured or infected area with the idea of quieting the inflammation and of checking the activity of bacteria, but it also lessens the resistance of the tissues of the patient, and by so doing may do more harm than good. Fauntleroy (1912) believes that in some cases of appendicitis the ice-bag is responsible for poor walling-off of the lesion and poor resistance on the part of the patient, as shown by the failure of the leukocytes to increase much above the normal.

Dry-cupping is a process of suction applied to the skin by means of specially made cups or small tumblers in which a vacuum is created. There are several methods of obtaining the vaccum, such as swabbing out the cup with a cotton probe dipped in alcohol and then lighting the alcohol, or igniting some cotton stuck in the bottom of the cup. The cup must be instantly applied; and in order that it may hold and perform its suction, its application must be in a region where the tissues are soft enough to be drawn upon. Care should be taken not to burn the patient and not to leave the cups on long in one place. Dry-cupping is not now much employed because of its awkwardness, but in extreme cases, as in edema of the Jungs or suppression of urine, may be resorted to.

Drugs

These are all, in the nature of the case, general protoplasmic irritants. The rubefacients are: camphor, menthol, and chloral hydrate, any two of which solids, when mixed together, become liquefied; the spirit and liniment of camphor, alcohol, chloroform, methyl salicylate (the liquid stearopten which composes over 90 per cent. of oil of wintergreen or oil of birch), oil of turpentine, tincture of iodine, ammonia, capsicum, and mustard.

The epispastics are: ammonia water (used by dentists for blistering the gums) and cantharides cerate.

Mustard (sinapis) is the ground seed of black mustard (sinapis nigra). Its use depends upon the development of an irritant volatile oil when the mustard flour is mixed with water. (See Glucosides, Part I.) It may be employed in the form of a mustard-leaf (charta sinapis) dipped in tepid water, or as a thin mustard paste made by wetting a mixture of mustard and flour with tepid water and wrapping in cheese-cloth. For an adult the paste may be made of one part of mustard to two or three of flour, according to the sensitiveness of the skin; for a child, one part to four or five of flour. A mustard paste usually reddens sufficiently in ten to thirty minutes, and its effect must be watched to prevent blistering. As soon as the skin is thoroughly reddened the mustard should be removed. Sometimes with the idea of preventing blistering, white of egg is mixed with the paste, or vaseline is smeared over the skin at the site of application. Whether or not such measures are efficacious we are unable to say. In pelvic congestion with suppressed menstruation a mustard foot-bath is sometimes employed. It is made by adding a tablespoonful of mustard to four quarts of warm water. A mustard-bath for infants is prepared of half this strength. In all mustard preparations very hot water should not be used, as this destroys or retards the activity of the enzyme which forms the irritant volatile oil. The enzyme is destroyed at 6o° C. (140o F.). It is to be borne in mind that the "hotness" of a mustard-bath should be entirely due to the mustard oil developed, and not to its temperature as recorded by the thermometer. Cases of poisoning by mustard give the symptoms of volatile oil poisoning. (See Carminatives.)

Cantharides (cantharis) is the dried and powdered brilliant green beetle, Cantharis vesicatoria, or Spanish fly. Its active constituent is 0.6 per cent. of cantharidin, an acid anhydride which forms soluble salts with alkalies. The "fly-blister" is a piece of adhesive plaster spread with cantharides cerate. About its only employment is in large inflammatory collections of fluid in the knee-joint, as in acute rheumatism. A fly-blister about two inches in diameter is applied to the skin for twenty minutes, then removed, and replaced by a flaxseed poultice. A large amount of serum collects beneath the skin and is removed by pricking the skin.

Internally, the 10 per cent. tincture has been employed as an emmenagogue in dose of 5 minims (0.3 c.c.). From its use to produce abortion, and its administration with the fancied purpose of stimulating sexual feeling, many poisoning cases have resulted.

It is a violent irritant, the symptoms following large or undiluted doses being local irritation in mouth, esophagus, stomach, and intestines, resulting in inflammation, blistering, or ulceration, with vomiting, diarrhea, bloody stools, and cramps. The kidneys and bladder also show intense inflammation, with bloody urine or suppression of the urine. There is sometimes priapism. Pregnant women may abort. The patient may go into profound collapse, resulting in death. The treatment is symptomatic, demulcents being administered by mouth and rectum, and collapse treated as described later.

Therapeutics Of Counterirritants

I. To relieve pain - muscular, neuralgic, and joint pains, as well as those associated with visceral affections (pleurisy, cardiac pain, biliary and intestinal colic, and dysmenorrhea).

2. To relieve congestion and inflammation - as in the case of inflamed lymph-nodes, pelvic congestion, and pneumonia.

3. To promote absorption - as of serous effusions in the pleural or peritoneal cavities or joints, in hydrocele, and in bruises or hematomata.

4. To overcome tympanites - as in the use of the stupe in typhoid fever or postoperative intestinal paralysis.

5. To overcome collapse - as in the use of mustard-bath or alternating hot and cold plunges for infants.

6. To check nose-bleed - ice to the back of the neck.

7. To relieve cerebral congestion - as the ice-bag in headache, delirium, meningitis, etc., or the menthol pencil in headache.

Cautions

Debility and old age, in which conditions irritants of all kinds tend to be depressing.