8 4 4 



ANIMAL HEAT. 



THE MEASUREMENT OF HEAT PRODUCTION. 



The amount of heat produced by an animal can be determined by 

 the measurement of the heat given off, and also by an estimation of the 

 heat value of the chemical changes taking place in the body. The most 

 exact method is that which embraces both of these determinations. 



Numerous attempts have 

 been made to construct 

 suitable calorimeters, but 

 it is only within the last 

 few years that exact 

 methods have been de- 

 vised. 



Calorimeters. 1 In 

 1780, Lavoisier and Lap- 

 lace 2 employed the ice cal- 

 orimeter, in which the heat 

 produced by the animal is 

 estimated from the amount 

 of ice liquefied. The con- 

 struction of this calorimeter 

 is shown in the accompany- 

 ing diagram. (Fig. 81). 



Important results were 

 obtained by the use of this 

 method, but they were not 

 an exact measure of the 

 heat produced by a normal 

 animal. The exposure to 



FIG. 81. Diagram of ice calorimeter. 



such a low temperature causes an abnormal loss and production of heat, and 

 it is impossible to rapidly and completely collect the water formed by the 

 melting of the ice. 



Crawford, 3 in 1788, introduced the water calorimeter, and indicated the 

 precautions necessary to obtain accuracy. The method was improved by 

 Dulong and Despretz. 



Although this calorimeter was a great advance upon the ice calori- 

 meter, yet it has been found by numerous observers to be unreliable. It 

 is impossible, even by careful mixing, to obtain the exact heat of the water, 

 for strata of different temperatures are formed, and thus errors easily 

 arise. Further, the water responds very slowly to any change in the 

 production of heat by the animal. This method was used by Dulong 4 

 and Despretz, 5 and has been again brought into use by Wood, Reichert, 

 and others. 



The air calorimeter appears to have been first used by Scharling 7 in 1849, and 



1 A list of researches in which different kinds of calorimeters have been used, will be 

 found in the paper by Haldane, Hale White, and Washbouru, Journ. FhysioL, Cambridge 

 and London, 1894, vol. xvi. p. 124. 



2 Hist. Acad. roy. d. sc., Paris, 1780, p. 355. 



3 " Experiments and Observations on Animal Heat," London, 1788, 2nd edition. 



4 Ann. de cliim. etphys., Paris, 1843, Ser. 3, tome i. p. 440 ; Compt. rend. Acad. d. sc., 

 Paris, tome xviii. p. 327. 



5 Ann. de chim. etphys., Paris, 1824, Ser. 2, tome xxvi. p. 337. 



6 Wood, "Fever," Smithson. Contrib. Knowl., Washington, 1880 ; Reichert, Univ. 

 Med_. Mag., Philadelphia, 1890, vol. ii. p. 173. 



7 Journ. f. prakt. Chew,., Leipzig, 1849, Bd. xlviii. S. 435. 



