554 Prof. H. L. Callendar on Electrical 



wire may be protected by cementing over it a thin film of 

 celluloid ; but a better plan is to insert the thermometer in 

 a thin flat celluloid sheath, as illustrated in fig. 7, which can 

 be changed at any time if it becomes soiled. The flexible 

 leads are flattened and insulated between celluloid films at 

 the end where they join the thermometer coil. In applying 

 the thermometer to the surface of the body, a truss, similar 

 to that employed by Dr. Gamgee (loc. cit.) for thermo- 

 couples, may be used ; but, in my experience, a simpler and 

 more generally applicable method is to back the thermometer 

 with a pad of cotton-wool to secure good contact, and to 

 keep it in place by means of an elastic band to which the 

 thermometer and leads are pinned or sewn. When the 

 thermometer is placed in the left axilla, which is generally 

 the most convenient location, the elastic band should pass 

 under the left arm, and over the right shoulder near the 

 neck. 



Fig-. 7. 



I« — 4 eovtt.- 



Axilla or Surface Thermometer (Celluloid). 



A surface thermometer of this type is extremely sensitive, 

 and shows no appreciable lag when placed in a water- bath. 

 But when placed in the axilla, or elsewhere on the surface 

 of the skin, it may take fifteen minutes or more to reach a 

 steady temperature. The reason of this is partly that the skin 

 is slightly chilled by exposure during the insertion of the 

 thermometer, and partly that the application of the thermo- 

 meter with its wool pad tends to raise the temperature of 

 the skin locally by preventing evaporation. The temperature 

 of the skin under normal conditions with free evaporation 

 is generally lower than that of the body. If the patient is 

 already in bed and well covered up, the initial lag may be 

 greatly reduced, but is in any case of little or no consequence 

 for records of long duration. 



A thermometer of this type should not be heated to 100° C. 

 or directly exposed to water at temperatures as high as 50° C, 

 because this procedure is liable to buckle the film. If the 

 temperature coefficient of the wire is known, it can be cali- 



