832 ANIMAL HEAT. 



variation of the temperature of the body, in the rise of temperature 

 observed after exercise, and during residence in tropical climates. 



The regulation of temperature, therefore, embraces two processes 

 regulation by varying loss of heat, regulation by varying production of 

 heat. 



The regulation of heat production. In considering the regulation 

 of heat production, it is necessary to trace out briefly the various 

 discoveries which have established, as a fact, that animal heat is due 

 to combustion within the tissues. 



Historical account of facts and theories upon the sources of 

 animal heat. 1 The ancients considered animal heat to be beyond the reach 

 of physical and chemical laws. They c^mld assign no cause for it, and there- 

 fore looked upon it as some innate quality, something essentially "vital." 

 This " vital " heat was supposed to be concentrated in the heart (Plato, Aris- 

 totle, Galen), and to be distributed to the body by the blood in the veins. It 

 was prevented from accumulating by respiration, the chief function of which 

 was to cool and temper the blood. 



As knowledge in physical and chemical processes increased, attempts were 

 made to give a rational explanation of animal heat. It was well known that 

 heat arose during fermentation, and by the contact of acid and base ; animal 

 heat was therefore considered to arise by some similar process or processes 

 taking place in the blood. Willis, 2 about the year 1670, put forward the 

 theory that there is in the blood a combustion which depends upon the fer- 

 mentation excited by the combination of different chemical substances. Fric- 

 tion was another well-known source of heat, and was the explanation given by 

 Boerhaave ; 3 he considered that animal heat was due to the friction of the 

 blood corpuscles in the vessels. Stephen Hales 4 adopted this theory, and gave 

 certain experiments, which he thought supported it. 



A much more correct opinion had already been formed in 1674 by Mayo w, 5 

 who, after his experiments on the constitution of air and its relation to the 

 heat of combustion, extended the analogy of combustion to animal heat. He 

 held that the function of the lungs was not to cool the blood, but to enable 

 that fluid to absorb the nitro-aerial gas (oxygen) of the air, and so generate 

 heat. 



Later research has shown that the heat of living things is not due to any 

 mystical so-called "vital" force, but to the processes of combustion, which 

 form one of the most important phenomena of life. The different steps by 

 which this knowledge has been attained are found in the discovery of Black, 6 

 that carbon dioxide was produced in animals by a process of combustion ; in 

 the work of Lavoisier 7 and Crawford, 8 who showed that the heat of an animal 

 might be accounted for by the processes of combustion ; in the researches of 

 Dulong 9 and Despretz, 10 whose results, when critically examined and explained 

 by Liebig, 11 formed an important support for the law of the conservation of 

 energy. 



1 Accounts of the old theories will be found in C. Bostock, "Essay on Respiration" ; 

 "An Elementary System of Physiology," 2nd edition, 1828, vol. ii. p. 243 ; Gavarret, 

 " De la chaleur produite par les etres vivants," Paris, 1855 ; and " Les phenomenes phy- 

 siques de la vie," Paris, 1869; Lorain, "De la temperature du corps humain," Paris, 

 1877, vol. i. p. 39; Rubner, Ztschr. f. Eiol., Miinchen, 1893-94, Bd. xxx. S. 73. 



- "De Accensione Sanguinis." 3 " Aphor. cum Notis Sweiten," pp. 382, 675. 



4 "Statical Essays," 2nd edition, 1733, vol. ii. p. 90. 



5 "Tractatus Quinque," Oxonii, 1674. 



G " Lectures on Chemistry," edited by Robison, Edinburgh, 1803. 

 7 Hist. Acad. roy. d. sc., Paris, 1777. 



8 "De calore Animali," 1779; "Experiments and Observations on Animal Heat," 

 1788. 



9 Ann. de chim. etphys., Paris, 1843, Ser. 3, tome i. p. 440. 

 10 Ibid., 1824, Se"r. 2, tome xxvi. p. 337. u "Thiercheinie," S. 28. 



