96
ELEMENTS OF MATERIA MEDICA.
thereby affect remote parts ; such are arsenious acid, and the Uchloruretof mercury.
Caustics are employed for various purposes, the principal ofwhich arethe following:—to remove excrescences or morbid growths of various :kinds, such as warts, condylomata, some kinds of polypi, aid spongygrowths or granulations ; to decompose the virus of rabid aiimals andthe venom of the viper, and other poisonous serpents; to fom artificialulcers, as issues; to open abscesses; for the cure of hydncele theyhave been applied to the scrotum, so as to penetrate through he tunicavaginalis; to change the condition of ulcerated and other surfaces; lastly,caustics are applied to strictures of the urethra.
Class 9. Rubefacients, Vesicants, and Suppurants. —Ihese areagents which, when applied to the skin, cause redness, and lometimesvesication and suppuration. The milder ones, such as frbtion andwarm fomentations, stimulate the skin temporarily, without iroducingactual inflammation. The stronger ones, such as mustard aid cantha-rides, excite active inflammation. Those that cause the exhalition of athin serous fluid beneath the cuticle are called vesicants or ejispastics:mustard, euphorbium, mezereon, acetic acid, ammonia, and caitharides,are of this kind ; while tartar emetic, and some other substan;es whichproduce a secretion of pus, are denominated suppurants. The nedicinesof this class are employed as counter-irritants in various diseases. Theirgeneral mode of operation has been before investigated (p. 45, tt seq.)
Class 10. Acids. —The mineral acids, in a concentrated state, arepowerful caustics; and, when swallowed, act as corrosive poisons;somewhat diluted and applied to the skin, they produce ruiefaction.Administered internally, in moderate doses, they act as tones, refri-gerants, and diuretics; but by long-continued use they disorcer diges-tion, and produce emaciation. When, from any cause—suci as dis-ordered digestion, particular kinds of food, or improper medicines—whitesand (either phosphate of lime or phosphate of ammonia and nagnesia,)appears in the urine, the internal use of acids will, in most cases, dimi-nish or remove it. They are improper, however, when there is muchirritation in the urinary organs.— [For further observations on the modusoperandi of the acids, see page 9.]
Class 11. Alkalies. —Applied in a concentrated form, tin alkalinesubstances act as powerful caustics, and, when swallowed, become cor-rosive poisons. Somewhat diluted and applied to the skin, they are !rubefacients. Taken internally they neutralize any acid whicl may befound in the stomach, and hence have been termed antacids ( mtacula ), .
or absorbents ( absorbentia ), and usually operate, when exhibitel in mo-derate doses, as diuretics. By continued use they disorder digestion,render the urine alkaline, produce general debility, and give rise tosymptoms similar to scorbutus. In such cases it is said that he blooddrawn from a vein does not coagulate on cooling, but remains ii a liquidstate ; and that if the use of the medicine be suspended, the blood againacquires its power of coagulation. By the continued admiiistrationof alkaline medicines the urine loses its acid properties, aid occa-sionally becomes decidedly alkaline ; and, in such cases, white land (thephosphates) is usually deposited: hence, where a phosphatic diathesisalready exists, these substances are highly improper. On the contrary,when the urine contains a larger portion than usual of uric acid, the useof alkalies is highly beneficial.