Used externally, it acts as a counter-irritant, and should not be painted on too freely as it may cause blistering. Does good if painted over swollen joints or enlarged glands, but should not be applied if the skin there is broken. Tincture of iodine may be painted on the chest or over the liver or spleen if there is pain. It is a valuable application for all open, recent wounds, and may be painted freely over and round the raw surface. It relieves the irritation of mosquito bites. Is very useful in certain diseases of the skin, such as ringworm, kraw kraw, and dhobie itch. _Iodoform powder_ is a valuable antiseptic, and is used for all kinds of sores, or wounds, in which it rapidly promotes healing. One part of iodoform to eight parts of vaseline makes a good healing ointment. _Ipecacuanha._—Dose, expectorant, half to two grains. ” emetic, fifteen to thirty grains. ” for dysentery, twenty to forty grains or more. In small doses, _e.g._, a quarter to half a grain, is a stomachic and may check vomiting. Was formerly much used in amœbic dysentery (p. 187). Its active principle, emetine, is now employed. By causing free expectoration, it is very useful in bronchitis, and is then usually combined with ammonia. Is contained in Dover’s powder, and in this form is useful in coughs and colds, as it helps to cause sweating. _Iron._—Iron is much used on account of its tonic and blood-forming properties. It is especially useful in anæmia following fevers and other exhausting diseases, and it also gives tone to the nervous system. Most preparations of iron are astringent in their action, some such as the sulphate and perchloride being more so than others; these are, therefore, useful in diarrhœa and in bleeding from the gums and bowel. Iron by its astringent action may cause constipation, and it may be necessary to add a small amount of an aperient, such as Epsom salts, to each dose. The following preparations are those generally used:— _Tincture or perchloride of iron, or tincture of steel._—Dose, five to fifteen drops in at least an ounce of water. Good blood tonic. Is very astringent, and is therefore useful in internal bleeding and looseness of the bowels. It is of value in erysipelas. _Sulphate of iron._—Dose, one to three grains. Is a powerful astringent and blood tonic, and often does good in checking the looseness of the bowels which remains after an attack of dysentery. _Iron pill or Blaud’s pill._—Dose, five to fifteen grains. Is one of the best tonic preparations of iron, as it is not very astringent. It is put up in tablet form. _Solution of dialysed iron._—Dose, ten to thirty drops. Is a good blood tonic, and, unlike most preparations, is not astringent. _Parrish’s food._—Dose, thirty to a hundred and twenty drops in water. Is a good preparation of iron for children.