In the constipation of delicate persons, especially of pregnant women, also of those subject to gout or rheumatism, hemorrhoids, or other rectal affections, magnesia is a valuable mild laxative; if required frequently, it should be taken in solution (fluid magnesia), and with lemon-juice, if the system be free from acidity. The citrate or two preparations are mixed only at the time of their being required: hydrated peroxide of iron is precipitated, and sulphate of magnesia remains in solution - 4 to 6 dr. of this should be given every quarter of an hour in warm water (Binz).

The sulphate are useful aperients at the commencement of a febrile attack of almost any kind, their action being rapid and more or less depletory; the former may be given effervescing in mild cases, but when a full and decided effect is desired, 1 or 2 dr. or more of the sulphate should be used; sometimes it is given in lemonade or acid infusion of roses, but general experience has proved that it acts best with tincture and infusion of senna. In habitual constipation 1/2 to 1 dr. given in a glass of lemonade or aromatic water, in the early morning, will often answer every purpose. Dr. Fleming found the addition of small quantities of atropia advantageous (British Medical Journal, ii., 1865): it is more usual now, and I believe better, to make use of the magnesian salts in combination with others, as they are found in many natural mineral waters, such as Seidlitz, Pullna, Friedrichshall, or Hunyadi Janos, half a glass or a glass of such waters being ordered with warm water in the early morning. To obviate constipation and headache during the use of astringent tonics, moderate doses of the sulphate may be usefully added to medicines containing sulphate of quinine, iron, acids, etc.