One of the main drawbacks in the paraffin method is the inconvenience of melting the paraffin and keeping it melted at the proper temperature, between 55 and 60 C. This is almost impossible by direct heat, since this would tend to overheat, and would also cool too rapidly. The device ordinarily used is a double boiler (cereal boiler). This answers, but is far from ideal. For simple dressings, as in office practice, it is inconvenient. With extensive dressings, as in shop practice, there is the further difficulty that the paraffin will either overheat or cool unduly while the attention of the surgeon is centered on the patient. The temperature could, of course, be kept constant by the ordinary scientific thermostats, but these are not practical, since they are too cumbersome, are immovable and are easily injured. Under the stress of war practice, the difficulties must be still greater.