Hydroquinol - Hydroquinone- Hydrochinone - Paradioxybenzene. - Colorless, odorless, dimorphous crystals, having a sweetish taste. Soluble in 17 parts of water, very soluble in hot water, alcohol, and ether. Dose, 1 1/2-5 grains (0.03-0.30 Gm.).

Catechol - Pyrocatechin - Orthodioxybenzene. - Acicular crystals, readily soluble in water, alcohol, and ether.

Other allied compounds are - thioresorcin, resopyrine, and fluorescein.

Physiological Action. - Pyrocatechin, resorcin, and hydroquinone, ortho-, meta- and paradioxybenzols, agree practically in all their actions. Pyrocatechin and resorcin are comparatively soluble in water. Hydroquinone is less so. They irritate the central nervous system, more particularly the spinal cord. Resorcin is the least irritating and poisonous of the three; 10 Gm. has been taken without causing death. Pyrocatechin is the most active, both locally and internally. It is more poisonous than phenol.

Therapeutics. - Externally and Locally. - Resorcin is especially useful in certain subacute or chronic skin affections, and may be used like salicylic acid in indurated eczema. It is of great value in psoriasis, seborrlicea sicca, pityriasis capitis, sycosis, acne rosacece, etc.

A 5 to 10 per cent. solution is an efficient application in pharyngitis, diphtheria, and ulcerative laryngitis. An ointment of resorcin is an excellent application to foul ulcers, sloughing wounds, and syplulitic ulcers.

Condylomata have been cured by dusting upon them powdered resorcin.

A mixture of powdered resorcin and boric acid (1:20 or 1:10) has been used with brilliant results in suppuration of the middle ear.

A 2 per cent. solution has been found useful in the form of a spray in whooping-cough, while stronger solutions of 10 or 20 per cent. have been used with some success in hay fever.

Solutions of resorcin have been used in gonorrhea and cystitis.

Internally. - Resorcin is preferable to carbolic acid for internal administration, especially in digestive disorders, such as gastralgia, chronic gastritis, ulcer of the stomach, and fermentative dyspepsia, so called. Owing to its sedative and antifermentative properties, it is of value in acute diarrhea of children.

It has been used with some success in intermittent fever, but not with good results sufficiently uniform to justify the exclusion of quinine. As an antipyretic it may be used when a drug of that character is indicated, but it is not equal to antipyrine or acetanilid, and in doses sufficient to produce the desired reduction of temperature it is too depressant to the heart. Its chief therapeutic value is for external or local use, and internally for the digestive disorders above mentioned.

Administration. - It should be given in pills or capsules.

The trioxybenzols, C6H3(OH)3, pyrogallol (1, 2, 3), oxhydro-chinon (1,2, 4), and phloroglucin (1,3, 5), are occasionally used in medicine. Pyrogallol is widely employed as a hair dye, is also employed in the treatment of psoriasis, and widely used in photography. It is highly poisonous. It behaves in a large measure like phenol, but in addition has a marked destructive action on the blood. Oxyhemoglobin is changed into methemoglobin and hemolysis also is energetic.

Phloroglucin used internally causes a peculiar type of diabetes.

Other hydrocarbons of this general group, such as benzol, toluol, xylol, are liquids and not useful, but naphthalin, a solid member of the series, and some of its derivatives, are therapeutically possible.