ANIMAL HEAT 



493 



purposes, especially if the bulb is flat or in the form of a flat spiral, 

 which can be easily applied to the surface. A theoretically better 

 method, but more laborious in practice, is the use of a thermo- 

 electric junction, or a resistance thermometer formed of a grating 

 cut out of thin lead-paper or tinfoil (Fig. 138). This is especially 

 useful for comparing the temperature of two portions of skin. The 

 temperature of the solid tissues and liquids of the body may also be 

 measured or compared by the insertion of mercurial or resistance 

 thermometers or thermo-electric junctions (p. $70). 



Galorimetry. The quantity of hea^ given off by an animal is 

 generally measured by the rise of tem- 

 perature which it produces in a known 

 mass of some standard substance. 

 Sometimes, however, as in the ice- 

 calorimeter of Lavoisier and Laplace 

 and the ether calorimeter of Rosenthal, 

 a physical change of state in the one 

 case liquefaction of ice, in the other 

 evaporation of ether is taken as token 

 and measure of heat received by the 

 measuring substance, the number of 

 units of heat corresponding to liquefac- 

 tion of unit mass of ice or evaporation 

 of unit mass of ether being known. 

 The unit generally adopted in the 

 measurement of heat is the quantity 

 required to raise the temperature of a 



kilogramme Of water I C, which is 



called a calorie, or kilocalorie, or large . 



Calorie. The thousandth part of this, of temperature causes an increase 



the quantity needed to raise the tern- in the resistance of the lead. The 



/ r balance of the bridge is thus dis- 



perature of a gramme of water by i , turbe d. By experimental gradua- 

 is termed a small calorie or millicalorie. tion the temperature value of the 

 In the calorimeters which have been tl &. ?& 

 chiefly used in physiology either water j p . S34 ). 

 or air has been taken as the measuring 



substance. The most convenient form of water calorimeter is a box with 

 double walls, the space between which is filled with a weighed quantity 

 of water. The animal is placed inside the vessel, and the temperature 

 of the water noted at the beginning and end of the experiment. 

 Suppose that the quantity of water is 10 kilos, and that the temperature 

 rises one degree in thirty minutes, then the amount of heat lost by 

 the animal is 10,000 small calories in the half-hour, or 480,000 in 

 the twenty-four hours ; and / r the rectal temperature is unchanged, 

 this will also be the amount of heat produced. Here we assume 

 (i) that all the heat lost by the animal has gone to heat the water, 

 and none to heat the metal of the calorimeter ; (2) that none has been 

 radiated away from the outer surface of '..ie latter. The first assump- 

 tion will seldom introduce any sensible error in a prolonged physio- 



138. RESISTANCE THER- 

 MOMETER FOR MEASURING 

 TEMPERATURE OF SKIN. 

 G, grating of lead-paper, attached 

 to a cover-slip, and mounted on a 

 W, wires to the 

 bridge. An 



