Dry Heat is most conveniently applied by means of hot water bags. They are made in all sizes from one holding a few ounces to one holding two quarts or more. It is often advisable to have a flannel bag into which the rubber bag easily slips; this is more comfortable to the patient and at the same time a safe-guard against burning.
Dry heat may also be applied locally by a hot brick or a hot iron wrapped in flannel, or best of all, by a hot sand Ironing is another very convenient method of applying heat, particularly useful in myalgia. A folded blanket is placed upon the bare skin and an ordinary flat iron as hot as can be borne is passed back and forth over the blanket.
Moist Heat, besides relieving pain and changing the flow of blood in inflammation, is very useful in causing relaxation in painful spasmodic conditions, as intestinal, renal, and biliary colic. It is also useful in retention of urine, from sluggishness of the bladder. In these conditions cloths wrung out of hot water and applied over the area of trouble frequently give marked relief.
The simplest method of applying heat locally is to immerse the affected part in hot water. This is, how-ever, seldom practicable except in the form of the foot bath.
A Dry Compress is the form of application in which the body supplies its own heat. Several layers of cotton or gauze are applied to the part, and covered with an impervious material such as oil silk, rubber tissue, or paraffine paper, and the whole is then firmly bandaged.
A Wet Compress differs from the above only in that the gauze or cotton is wet when applied. The solution much used for this purpose is a 1:2000 Bichloride of Mercury, which makes an antiseptic poultice. If, however, the dressing is to bo applied for more than a few hours a strength of 1 :3000 or 4000 is preferable, as it can cause derma titis. Another efficient solution, and to be preferred if there is no infection to combat, is a mixture of alcohol and water in the proportion of 1:3. This is efficient in reducing localized swelling.
Poultices are often best, used as a mixture of kaolin and glycerin, if there is no open wound. There are several such preparations on the market and the eighth revision of the Pharmacopoeia makes Cataplasma Kaolini official. It contains kaolin (57.7 per cent.), glycerine, boric acid, methyl salicylate, thymol, and oil of peppermint.
Very useful is the old-fashioned flaxseed poultice, if there is no wound or open ulcer. This is prepared by stirring flaxseed meal into boiling water, adding the meal in small quantities and stirring continuously until the required consistency is reached, i. e., as thin as it is possible to make it without its pouring. The paste should be spread upon several layers of gauze, the thickness of the poultice being not less than 3/8 of an inch. The poultice should be renewed as often as it is necessary to keep it hot, and this will be about every three or four hours. A covering of oil silk, paraffine paper or rubber will increase the length of time that the poultice holds its heat. Several thicknesses of flannel serve the same purpose to a less degree, or better, the hot water bag.