Ichthyol and thiol are oily-looking sulphur compounds which are soluble in water and the oils, and not in alcohol. Ichthyol is obtained from a shale, and thiol is prepared synthetically. Their 3 to 5 per cent. solutions are applied externally as soothing lotions, as in bad sunburn. Their 50 per cent. solution is painted over infected areas to promote absorption of serous or fibrinous exudates. Ichthyol ointment, 10 to 50 per cent., is applied to lessen glandular or joint swellings and in erysipelas. It has been thought that it may favor the resistance of the tissues by inducing a local gathering of leukocytes. Vaginal tampons bearing a solution of 10 to 30 per cent. in glycerin are largely employed in cases of chronic endometritis and chronic pelvic inflammations. Ichthyol has an unpleasant odor, while thiol is nearly odorless.

Internally, ichthyol is employed in cases of intestinal putrefactive toxemia as an intestinal disinfectant, dose, 3 to 5 grains (0.2-0.3 gm.) in a capsule or enteric pill. It is slightly laxative. Ichthyol enters into "Bum Mixture." (See Hoffmann's Anodyne.)

Methylene-blue (methyl-thionine chloride) is little used as an antiseptic. It turns the urine a bluish-green, a fact that has been made use of as a functional test for the kidneys. It has been injected into recurrent or inoperable carcinomata, but without any noteworthy effects. After its ingestion by mouth Brauer found large quantities of it in the bile. The ordinary commercial article usually contains zinc, and if taken internally may cause vomiting. The author saw a case of acute gastroenteritis follow a capsule of methyl-blue, prescribed by the physician in mistake for methylene-blue.

Formaldehyd (Hcoh) is a gas, and its aqueous solution, containing not less than 37 per cent. by weight of absolute formaldehyd, is official under the name of "Liquor Formalde-hydi." This solution should be neutral or only faintly acid to litmus, showing the absence of formic or other acids. It is marketed under the name of "Formalin," and usually contains about 10 per cent. of methyl alcohol to facilitate solution and prevent polymerization. At ordinary temperature it gives off formaldehyd gas. On cooling the solution below 68° F., a white powder results. This is known as paraformaldehyd (paraform, trioxymethylene), and is a polymeric form of formaldehyd. On gently heating, this is reconverted into gaseous formaldehyd.

Formaldehyd is pungent and very irritating to eyes, nose, and throat. It is rendered inert by alkalies, especially ammonia; it reduces Fehling's solution; it attacks metals (instruments); it hardens tissues, blood, and gelatin (blood on the hands becomes darkened and difficult to wash off). This last property has been made use of to harden gelatin capsules so that they would pass through the stomach into the intestine before dissolving (glutol capsules); but the degree of hardening is uncertain. It is employed as a hardening and fixing agent for anatomic and biologic specimens, and is used as an arterial injection for embalming the dead and for preserving cadavers for dissection. It may be employed for fixing blood-smears. . An important property is that of preventing the coagulation of serum albumin by heat, as in urine.

Formaldehyd is a powerful disinfectant. It is much employed as a preservative of foods. One part in 20,000 cannot be detected by its odor, yet will keep milk for several days. In 1: 50,000 strength it retards the growth of the lactic acid bacillus, but has little effect on the colon or typhoid bacillus (Vaughan). Bur-nam (1912) found that a 1: 20,000 solution retarded, but did not destroy, typhoid bacillus and streptococcus; but that a 1:1000 solution killed colon, typhoid, and pyocyaneus bacilli, streptococcus and Staphylococcus aureus in twenty-four hours. It is used as a preservative of cider, fruit-juices, and canned foods, and is employed as a valuable general disinfectant for sick-rooms.

The gas may be generated - (1) By warming the solution; (2) by heating paraformaldehyd; (3) by adding one pound of fresh quicklime to a mixture of 6 ounces of aluminium sulphate and 8 ounces of formaldehyd solution, as advised by the New York Health Department, this amount yielding enough gas to disinfect a room containing 1000 cubic feet; (4) but the best method of all is to add compressed blocks of potassium permanganate to the formaldehyd solution in a large pail. The gas is given off with violent ebullition (formanganate disinfector). (5) Lawall pours a mixture of 1 1/2 ounces (45 c.c.) of commercial sulphuric acid with 1 pint (480 c.c.) of formaldehyd solution over 9 ounces (270 gm.) of sodium dichromate crystals. This is cheaper than the permanganate method.

The exposure to the gas should be from twelve to twenty-four hours. It has little penetrating power, so may fail to enter the cracks in the floor or penetrate a mattress. In the presence of moisture, as steam, it is more effective than when dry. If the temperature of the room is below 52° F., it may polymerize into paraform. It does not kill vermin. Doty and others report that bedbugs, roaches, mosquitos, or even rats, rabbits, and guinea-pigs were alive after many hours' exposure. The gas is immediately neutralized by ammonia gas.

Formaldehyd is somewhat used for sterilizing absorbent cotton, sutures, and surgical dressings; but, on account of its action on metals, its irritating vapor, and its bad effect on the hands, is limited in its use as a surgical disinfectant.

Locally, the solution of formaldehyd has been used in fungous skin diseases (favus, sycosis, ring-worm), to disinfect foul ulcers and cancers, to check local sweating, and to harden and dry up small growths, such as moles, condylomata, and even cancer. Daniel says that formalin rubbed into warts with a stick makes them come off without leaving a scar. In very weak solution it has been employed as an antiseptic to mucous membranes, as in catarrh of the nose, throat, or vagina - usually with other mucous membrane antiseptics. Recently it has been recommended to leave a weak solution of formaldehyd in the pleural cavity after paracentesis for pleurisy with effusion.