DERIVATION.--Magnesium sulphate is a constituent of sea water and of
some saline springs. It also occurs native, either crystallized in
slender, prismatic, adhering crystals, or as an efflorescence on certain
rocks and soils which contain magnesia and a sulphate or sulphide. In
the United States it is found in the great caves so numerous to the west
of the Alleghany Mountains.
PROPERTIES.--Small, colorless, rhombic prisms, or acicular crystals,
without color and having a cooling, saline and bitter taste; slowly
efflorescent in dry air; .85 part of water; insoluble in alcohol.
ACTIONS.--Magnesium sulphate is a hydragogue and cholagogue cathartic;
alterative and febrifuge and is also feebly diuretic and diaphoretic. As
a cathartic it resembles common and glauber salts, and is more active
than potassium bitartrate or sodium phosphate. When magnesium sulphate
is administered it causes outpouring of secretion from the walls of the
small intestines, most quickly and abundantly when the bowels have been
partially emptied by several hours’ fasting. Neither pancreatic fluid
nor bile is materially increased. But magnesium sulphate has a low
diffusing power. It is slowly absorbed, and moreover, retards diffusion
and absorption of fluid present in the bowels. In this twofold action by
increased secretion and retarded absorption the fluid contents of the
bowels are increased, producing more or less mechanical distension and
provoking, like other salines, slight peristalsis. The retarded removal
of accumulating liquid is apt to produce the formation of gases in the
bowels, which is relieved by conjoining carminatives, as ginger or
capsicum, while effectual removal of the intestinal fluids is attained
by using with magnesium sulphate aloes, calomel or oil. It acts in from
twelve to sixteen hours; in small doses it stimulates the secretions of
the kidneys and skin. In febrile diseases it is used in small repeated
doses. It is valuable in treating animals suffering from reflex skin
irritation, combined with large doses of bicarbonate of sodium,
generally gives relief, especially in urticaria of the horse. It is
quite commonly used as a cathartic for horses, but most often for cattle
and sheep.
DOSES.--When repeated two or three times as a laxative and alterative
horses take 2 to 4 ounces, cattle 3 to 6 ounces, sheep and pigs, 1 to 2
drachms. As a cathartic cattle take 1 to 2 pounds, calves two to three
months old 3 to 4 ounces, sheep 4 to 6 ounces, dogs 1 to 4 drachms.
Aloes is a much better cathartic for horses, and castor or linseed oil
acts much better as a cathartic in pigs.