MEASURE OF HEAT PRODUCTION. 



847 



The respiratory exchange as a measure of heat production. 



The heat of the body has been shown to be due to processes of com- 

 bustion occurring in the tissues. The respiratory exchange is a measure 

 of this combustion, and hence a determination of the intake of oxygen 

 and the output of carbon dioxide is a measure, although not a perfectly 

 accurate one, of the heat produced. There is, however, one source of 

 inaccuracy in this method ; a determination of the respiratory exchange 

 during a limited time is not an exact indication of the combustion occur- 

 ring during that time, for we know that oxygen may be taken up and 

 stored in the body for a considerable period, and carbon dioxide may be 

 given off by the breaking up of previous combinations ; in fact, may still 

 be evolved when the tissues are receiving no free oxygen. Nevertheless, 

 consecutive determinations of the respiratory exchange for long periods, 

 and careful observations of the animal's temperature, form a most valu- 

 able method for the study of the regulation of temperature by heat 

 production, especially since calorimetric experiments are more tedious, 

 difficult, and more open to accidental sources of error. 



In the case of warm-blooded animals, a fall in external tempera- 

 ture increases, a rise diminishes the intake of oxygen and the out- 

 put of carbon dioxide. Crawford 6 and Lavoisier 7 came to this 

 conclusion not only on theoretical grounds, because they believed that 

 animal heat was due to combustion, but from the results of direct 

 experiment. 



1 Journ. f. prakt. Chem., Leipzig, 1849, Bd. xlviii. S. 435. 



2 "Recherches sur 1'equivalent mecanique de la chaleur," Paris, 1858 ; "Exposition 

 analytique et expe'rimentale dela the'orie me'canique de la chaleur," Paris, 1875, 3e Edition, 

 tome i. p. 27. 



3 Deutsches Arch. /. klin. Med., Leipzig, 1869, Bd. v. S. 273. 



4 Centralbl.f. d. med. Wissensch., Berlin, 1871 ; Arch. f. Aiiat., Physi-ol. 11. wissensch. 

 Med., 1872, S. i. ; 1874, S. 18; " Untersuch. ueber den lieberhaften Process und seine 

 Behandlung," Berlin, 1873, S. 30. 



5 Arch, de biol., Gand, 1887, tome vii. p. 276. 



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



7 Hist. Acad. roy. d. sc., Paris, 1780, p. 407. 



