Caustic potash* is a powerful caustic, and must be used with care, for it is extremely rapid in its action, and often this action is much deeper than was originally intended. The caustic stick should be employed rather than the solution, which may be accidentally dropped upon other parts than intended. Usually only one or two minutes' application is necessary, and the further action can be stopped by acetic acid or vinegar. The use of this caustic is extremely painful for the moment.
Arsenic, or rather arsenious acid, is undoubtedly the most popular caustic in the hands of the dermatologists. It is frequently employed in the form of Marsden's paste, which is made by using two parts of arsenious acid and one part of mucilage of acacia. Arsenic is supposed to have a selective action. It should never be applied to a surface more than one inch square because of the possibility of absorption and consequent poisoning. Either cocaine or orthoform is usually added to the paste to lessen the pain of application. It is usually allowed to act for from twelve to thirty-six hours, and a good deal of inflammation results. A slough results at the seat of application, which separates slowly. Many eminent dermatologists extol arsenic, Gottheil,* Marsden, Robinson,* Stelwagon, and others thinking very highly of it.
Silver nitrate is of value only after a thorough curetting, for its action is very superficial, owing to the formation of silver albuminate on the surface. Care should be taken to use only the pure molded silver nitrate, and not the ordinary lunar caustic, which is greatly inferior.
This caustic should not be used after cauterization; a more deeply-acting one should be selected. At times it may be used to stop oozing that results from the excision of a small neoplasm, but a touch with the actual cautery is much more efficacious. In reality this, as well as practically all other caustics, could be well dispensed with in cancer work.
Zinc chloride was formerly extensively employed by dermatologists, and still constitutes the basis of many quasi-can-cer pastes. This salt is very painful in its action, and destroys healthy or diseased tissue indifferently. Its action is peculiar in that it seems to dry up the tissue rather than corrode it. It is most commonly used in the form known as Bougard's paste, the formula for which is:
*Van Harlingen: Jour. Cutan. Dis., 1906, xxiv, 345. "Gottheil: Treatment of Skin Cancers, New York, 1899. "Robinson: Internat. Jour. Surg., 1892, 179.
Internat. Jour. Surg., 1893, 164.
New York Med. Record, Mar. 31, 1900.
H Farinae tritici (wheat flour),
Pulveris amyli, aa ...................................... 3ss
Pulveris arseni trioxidi .................................. gr. iv
Pulveris hydrargyri sulphidi rubri,
Pulveris ammonii chloridi, aa ........................... gr. xx
Pulveris hydrargyri chloridi corrosivi...................... gr. ij
Zinci chloridi crystallisati................................ 3iv
Aquae fervidae ........................................... 3j
The first six ingredients are mixed separately and the zinc chloride dissolved in the water, and the two parts then rubbed up together. It takes one or two days for any amount of destruction to take place, usually one or two applications being necessary. This prescription should appeal to those who still believe in polypharmacy, the "shotgun artists".
Formalin is extolled by Ravogli,* who first curettes and then applies it in equal dilution with cresol and perchloride of iron. He reports excellent results, some of his cases having been followed for many years.
In general, the author is not favorably disposed to the use of caustic pastes, except after either curettage or excision of the growth, or in the case of extremely old or feeble individuals. There is no doubt that many of the small basal-celled neoplasms can be destroyed by the use of a caustic paste alone, but the mere fact that very-many of the patients with cancer of the skin who have come to the Johns Hopkins Hospital surgical department for operation have had this method of treatment tried upon them is sufficient refutation of its universal efficiency. In these cases the report of the patients invariably was that the treatment was extremely painful, and that it left a large ulcer that was extremely difficult to heal. When these facts are explained to the patient, it is usually not difficult to secure his consent to an operation. In ten years' practice the author has not once had to resort to a caustic paste because the patient refused operation. As already pointed out, if a true selective action exists, which in many instances is doubtful, it makes the prognosis infinitely worse, because cancer cells are invariably found invading more or less deep down in the healthy tissue, the cancer cells existing in small groups. After operation, however, the use of a caustic upon the edges of the wound undoubtedly decreases the percentage of recurrences, and has now become almost a routine in the practice of the author.
*Ravogli: Amer. Jour. Surg., May, 1913.