MEASUREMENT OF TEMPERATURE 83 



The doctor's thermometer. For the measurement of the tempera- 

 ture of the body, what is termed a clinical tnermometer is best (Fig. 67). 

 As the temperature of the living human body is never many degrees 

 above or below a temperature of 98 F., a clinical thermometer is only 

 graduated from about 95 F. to 110 F. If the bulb of such a thermo- 

 meter is put into the mouth, or under the armpit, of a person in health 

 and left there for two or three minutes, it will be found, on taking it 

 out, to indicate a temperature from 97 '8 F. to 98 '6 F. The thread 

 of mercury in the stem of the thermometer remains in one position, 

 though the air is cooling the mercury while the thermometer is being 

 read. This is because of the constriction at the top of the bulb, which 

 causes the thread of mercury in the stem to be left behind while the 

 mercury in the bulb contracts. To " set " the thermometer for a 

 fresh observation, it is only necessary to jerk it slightly, when the 

 thread of mercury will again join up to the liquid in the bulb. 



