This instrument overcomes the complications of the water bath and burning or browning of the paraffin mixture, so commonly found with ordinary methods, the temperature of the resistance coil within the heating chamber being controlled by a small rheostat at will. Before using, the contents of each test tube thus prepared are reheated to sterilization and poured into the barrel of the syringe to two thirds of its length, the piston introduced and screwed down into position; the syringe being placed to one side until its contents have been cooled, or the entire instrument is immersed in sterilized water at about 70° F. until the paraffin mixture has set or becomes uniform in consistency, which takes about five minutes. Upon screwing down the piston the mass will be found to issue from the needle as a white, cylindrical thread, and is ready for use in this form. Harmon Smith has had such a paraffin prepared which has a melting point of 110° F. This can be purchased in the market in sterile sealed tubes ready for use. The contents of these tubes should, however, be resterilized at the time of employment. The same author prepares this paraffin of 110° F. melting point by mixing sufficient petroleum jelly (evidently white vaselin) with the commercial paraffin melting at about 120° F. to bring the melting point down to 110° F. He claims that making such a mixture is a difficult matter, since a plate of paraffin will have various melting points, one corner melting at 120° and the opposite as high as 140° F. He advises having the mixture accurately prepared in large quantities and dispensing it in test tubes of one-half ounce capacity, as now found on the market. The mixture is poured in hot liquid form into these test tubes, which are then sealed with wax and placed on a sand bath, whose temperature is raised to 300° F. to insure sterilization. The latter author has devised a neat paraffin heater, shown in Fig. 287. [Illustration: FIG. 287.—SMITH PARAFFIN HEATER.]