THE THERMOMETER 337 



of a tropical sea and ever since have had to maintain this initial 

 high temperature. The advantages that they possess by reason 

 of their higher temperature are due (a) to the well-known fact 

 that most chemical and some physical reactions are increased 

 in rate by heat, and (b) to their freedom from constant fluctuations 

 of temperature. Against this must be placed the fact that they 

 have to maintain a temperature greater than their environment 

 by about 20 C. 



Of all animals, birds have the highest temperature. For 

 example, that of the chicken is about 43-8 C.: of mammals, the 

 rabbit and the fox have a temperature as high as 40 C., while 

 the horse and the elephant come low on the scale with 37-6 C. 



In health, the temperature of the human body varies so little 

 from the normal value of 37 C. (98-4 F.) that temperature is 

 regularly taken as a clinical indicator and any fluctuation from 

 the normal points to the employment of remedial measures. 



Homoiothermic Animals maintain a constant temperature. 

 Mammals and Birds - Birds - about 42 C. 



Adult and not during hiber- /Mammals (except man) 39 C. 

 nation or activity - - \Man - " 37 C. 



Heter other mic or Poikilothermic Animals. 



(a) Lethal temperature, New born Homoiothermes. 



about 20 C. 



(b) Hibernation starts when Hibernating animals. 



temperature falls to 

 about 20 C. 



(c) Still active below 20 C. Keptiles, Batracia, Fish, Molluscs, 



Insects, etc. 



Instruments used. 



(a) Mercury thermometer. 



(b) Electrical resistance thermometers. 



(c) Thermo-electric couple (Thermopile). 



(a) The thermometer was probably invented by Galileo (1603), and was 

 first used clinically by Sanctorius (1626), who reported the temperature 

 of a fevered man. 



The clinical thermometer is an adapted form of the common mercurial 

 thermometer having, (1) a long cylindrical reservoir to admit of rapid 

 attainment of equilibrium between body and mercury. (2) A small 

 bulbous part just above the mercury reservoir to catch the mercury driven 

 out of the reservoir by the expansion due to the increase in temperature 

 to 34 C. (3) A small bore capillary graduated from 35 C. to 45 C. to 

 admit of reading to a tenth of a degree, and finally, (4) another bulbous 

 part to catch any mercury that might be driven over by accidental heating 

 beyond 46 C. Usually the thermometer is made self-registering by having 

 a small detached thread of mercury which is pushed up by the expanding 

 fluid and remains at the highest temperature reached. 



B.B. 22 



