V. TEMPERATURE DETERMINATIONS 161 



have been used successfully for many years in the walls of calorim- 

 eters and in other apparatus for the measurement of air and wall 

 temperatures, (d) Resistance thermometers have often been used 

 to measure surface temperatures. One type is the Dermalor of Fig- 

 ure 7 and a second type has been described by Soderstrom (26). 

 Bohenkamp (38) measured human surface temperatures by winding 

 resistance wire around various parts of the subject's body, (e) Re- 

 sistance thermometers can be used to measure the temperature of 

 plants, bacterial colonies, solutions, interfaces, and practically every 

 place where liquid-in-glass or large thermocoui)les are used. Like 

 thermocouples, they have the advantage over liquid thermometers of 

 being read m situ either near to or remote from the observer. (/) 



Fig. 13. Resistance type of rectal thermometer: (.4) lead; (B) and (C) 

 leads soldered together at tip of thermometer; (N) insulated nickel resistance 

 wire wound around three leads; (<S) silver shell; (R) rubber tubing covering 

 leads: (7") thread liinding rubber to silver shell, .\fter Soderstrom (£6). 



Resistance thermometers are particularly adaptable for use with elec- 

 trical recording apparatus and many direct reading and automatic 

 recording temperature devices are available on the market. 



Thermistors, in addition to many of the above applications, pos- 

 sibly can be used in rod form for intravascular temperature measure- 

 ment (Fig. 10). The probe type is useful in measuring ambient air 

 or liquid temperatures while the disc or pellet type can be easily in- 

 serted into a metal thermometer bulb. The disc form has also been 

 sweated onto metal plates to give a low thermal impedance connec- 

 tion to the object whose temperature is being studied. The large 

 disc form is enveloped in a paint finish for use in humid surroundings. 

 Minute beads with response times of less than a second in air and 

 flake thermistors with time constants from one millisecond to one 

 second have also been manufactured. These forms are useful for 

 temperatvn-e determinations of objects that are either inaccessible, in 

 motion, or too hot for contact thermometry. Radiation from the 

 object can be focused on the thermistor by means of a concave mirror. 



