This is prepared from oyster-shells, by first cleansing, then powdering, and lastly treating them by the processes of levigation and elutriation, as in the instance of chalk. The preparation is usually also in the same form of little cones. This differs from prepared chalk only in containing organized animal matter, intervening between the calcareous particles, so that, when the stomach acts upon it, the animal matter being dissolved, the oyster-shell is brought to the minutest possible state of division. This may render the preparation better adapted to an irritated stomach; and I have myself imagined that I have found it so in practice. At least, I generally prefer this form of carbonate of lime to any other for infants.

Medical Effects and Uses

Chalk and the analogous preparations unite a moderate astringency with a strong antacid power. Perhaps the astringency is not exactly of the same character as that of the vegetable astringents, but it at least promotes contraction of the tissues, diminishes the amount of secretion of the alimentary mucous membrane, and rather favours constipation of the bowels. Hence, this antacid is preferred to all others, when there is a coincidence of diarrhoea and excess of acid in the stomach and bowels. indeed, this complaint is not only attended with and sustained by acid matter, but not unfrequently has its origin in that cause, especially in infants. Hence, chalk is a favourite remedy in diarrhoea, and is much prescribed in almost all cases, where there is not evidence of acute inflammation, or high vascular irritation. The same indication sometimes exists in chronic dysentery with rather copious evacuations. in these affections, it is almost always associated with other medicine, at the same time indicated; often with opiates, often too with vegetable astringents and aromatics, and occasionally with a little blue mass or calomel, when the liver is torpid. These combinations are sometimes given in powder; but much more fre-quently in liquid mixture.

Prepared chalk is sometimes also preferred to other antacids, when, with acidity of stomach, there may be an apprehension of looseness of the bowels, without its positive existence.

It may seem strange that chalk should be disposed to restrain the bowels, while natural limestone water generally purges; as the carbonate of lime taken up is essentially the same as chalk in composition. But, in limestone water, the neutral carbonate has probably been changed into a soluble bicarbonate, which may be laxative.

Chalk is one of the best antidotes for oxalic and sulphuric acids.

Administration

The dose of chalk is from ten to forty grains. Fifteen to twenty grains is a suitable quantity for each dose of a compound chalk mixture. This dose, in urgent cases, may often be repeated every hour or two until the discharges are arrested. in ordinary cases, it is given three or four times a day.

An officinal Chalk Mixture (Mistura Cretae, U. S., Br.) is prepared, according to the U. S. directions, by rubbing together half a troyounce of prepared chalk, two drachms, each, of sugar and gum arabic, and eight fluidounces of a liquid composed equally of water and cinnamon water. A tablespoonful is the ordinary dose. in diarrhoea, an opiate, with or without kino or catechu in substance or tincture, may be associated with the mixture.

When the chalk is given in powder, it may be mixed with sugar and powdered cinnamon, with kino, catechu, or extract of krameria, and often with powdered opium or Dover's powder, according to special indications.