POTASSIUM, SALTS OF.—Potassium is an important element in the human body, and is usually obtained from various salts occurring in plants. The uses to which potassium is put in the human body are various. It is important in determining the alkalinity of the blood ; it plays a very important part in the process of clotting of the blood (see FILE\lOPH[LIA) ; and it is of great importance in regulating, in some unknown manner, the force and regularity of muscular contractions. The salts of potassium have a limited application in medicine, notwithstanding the importance of the element in the physiological economies of the body. The citrate, tartrate, nitrate, and sulphate are used ; but in their actions the potassium plays a minor role. See also PERMANGANATE OF POTASSIUM.
POTATOES.—The potato is an edible tuber of the Solanum tuberostim, a plant of the nightshade family. It is native to South America, whence it was introduced into Europe by Sir Walter Raleigh, in 1586. It is now extensively cultivated in all civilised countries. Prior to the seventeenth century, however, its worth was not appreciated ; and it was want and distress that finally made it a popular foodstuff. Potatoes are a welcome " stomach filler," especially among the poor ; while to the rich they furnish a side-dish with which they do not wish to dispense. As an exclusive diet, however, potatoes are not suitable. An enlarged abdomen and wasted, emaciated limbs characterise the unfortunates who are unable to supplement a potato diet with the amounts of albumin and fat necessary to health.
Although the soil and the ripeness of the vegetable greatly influence the composition of the potato, the average constituents are about as follows Water, 76 per cent. ; starch, 21 per cent. ; albumin, per cent. ; and slight traces of fat. On the other hand, potatoes are distinguished by their high percentage of potassium ; and for this reason they require a sufficient amount of common salt in their preparation for the table, since otherwise they will cause marked digestive disturbances. Such disturbances of digestion
are brought about also by potatoes that are insufficiently masticated or fried very hard. It is necessary to cook the potato in order to transform its starch, so that it mar be digestible. Potatoes are most readily digested when mashed, whereas fried potatoes are most indigestible. Potatoes always answer their purpose best when taken in combination with other foodstuffs. They can be especially recommended in combination with milk, cheese, eggs, or other albuminous foods, and also with some lard. Potatoes that are unripe, frozen, or diseased, as well as those that have sprouted, are unwholesome.
POTT'S DISEASE.—See BONE, INFLAMMATION OF.
POULTICES.—Mollifying remedies applied externally in order to exert a local action on the skin, and through that also upon deeper organs. According to the purpose for which it is applied, a poulice may be cold, warm or hot, dry or moist.
Dry, heated poultices may consist of cloths, hot-water bags, or of cushions filled with herbs or sand. Warm poultices should have a temperature of about F. ; hot poultices should he heated to qo' F. or more. These poultices are used to allay pain.
Moist, heated poultices are usually applied over the site of a local inflamma tion. A linen cloth is dipped into water of the prescribed temperature, and is applied to the affected part of the body. In order to preserve the heat of the poultice, the moist cloth is covered with woollen cloths or with hot-water bottles. Stearn-poultices are very popular. The affected part of the body is covered with flannel, on top of which is placed a cloth which has been heated with steam or immersed in steaming hot water. This is again covered with flannel or woollen cloths. Moist poultices may be made also from hot pap (potato-mash, linseed-flour, etc.). The pap in itself has no curative qualities ; it simply serves as a means of preserving the moist heat for a con siderable length of time.