ANIMAL HEAT. 



By DAVID FRASER HARRIS. B.Sc. (Lond. 

 Of the University. Binvuisihaiii . 



One of the most noticeable features of an animal is 

 that it can produce heat. Biologists long ago came 

 to the conclusion that it was h\- the oxidation chiefly 

 of the carbon and hydrogen in or by the li\'ing 

 substance that animal heat \\as generated. By 

 " long ago," we mean the time of the great chemist 

 Lavoisier, who, though he made some mistakes in 

 animal chemistry, certainly understood that animal 

 heat and the heat of combustion were alike in this 

 that they were both due to oxidations. Before the 

 discovery of oxygen bv Priestle\' and Lavoisier, this 

 position could not have been attained to. although 

 both Lower and Mayow of Oxford b\- 1669 had 

 arrived at the conclusion that there was something 

 in the atmosphere (Mavow called it " nitro-aerial 

 particles "') which was essential for the maintenance 

 of animal life, and for all sorts of combustions. This 

 was the dawn ; Priestle}' and Lavoisier were morning 

 stars : we live to-da\' in the high noon of the under- 

 standing of animal heat. 



The chemical view of the origin of animal heat 

 was, however, lost sight of by two such eminent 

 thinkers of the eighteenth centur\- as Boerhaave and 

 Hales, who held that the heat of the body was due 

 to the friction between the blood-corpuscles and the 

 blood, and between them and the walls of the vessels. 

 This is known as the iatro-ph\sical view of animal 

 heat. One can only mention the famous view of 

 Stahl (1687), that the " princijjle of fire was 

 phlogiston," a Teutonic '" will-o'-the-wisp " that 

 retarded the advance of thermo- and bio-chemistr\' 

 for quite a hundred years. 



But if h\ '"long ago" we mean the centuries 

 before the Christian era, we shall find that Aristotle, 

 for instance, who seems to have had something to 

 say on ever\thing in heaven and earth, taught that 

 animal heat was something absolutely unique. 

 Aristotle believed that animal heat was something 

 sui generis, something of an absolutely different order 

 from heat of non-vital origin — the heat of a fire, or 

 of a gas compressed, or of friction, for instance. He 

 thought that the ultimate source of bodily heat was 

 an eternal essence, the source of being of heaven and 

 the stars, which latter were imagined as intelligent 

 existences. 



This was, of course, the foundation of astrology, 

 the notion that these celestial intelligences could 

 interfere in human affairs, and were capable through 

 the harmon\- of their movements of creating music 

 — the " music of the spheres." 



For long after Aristotle's time the idea prevailed 

 that the blood, recuperated by the food in the 

 intestines, was kept fluid in the heart by the heat 



there ; but that the heart, becoming too hot, had to 

 have cold air sucked in h\ the lungs to cool it. 

 This teaching actually lingered until the time of 

 Har^■e\■ who died in 1657. 



Animal heat, as distinguished from every other 

 kind, was also thought to have quite special curative 

 powers. Thus we are told in the Book of Kings 

 that when King David " was old and stricken in 

 years. . . . they covered him with clothes but he 

 gat no heat." His servants recommended that a 

 N'oung girl should be brought to impart heat to him ; 

 " let her lie in thy bosom that my Lord the King 

 may get heat." 



Our present view is that one of the attributes of 

 li\-ing matter is to oxidise carbon and hydrogen to 

 form carbon dioxide and water, which process cannot 

 be effected without the evolution of a certain amount 

 of heat. Whether or not we are able to detect the 

 heat so produced is quite another matter. One of 

 Lavoisier's original ideas was that all the animal 

 heat was produced in the blood of the lungs ; that the 

 lungs were the furnace of the body, and that the 

 heat was carried thence by the circulating blood. 

 We now know that the blood is responsible for the 

 production of \ery little heat inileed, and are (juite 

 certain that it is in the muscles that by far the 

 greatest amount of bodih' heat is manufactured. 

 That a bloodless muscle could produce heat even 

 after it was cut out of the body was proved for the 

 first time by Helmholt/ in 184S. 



Evervone is familiar with the distinction between 

 cold-blooded and warm-blooded animals, but this 

 classification has lost its meaning. We now speak 

 of animals which are able to maintain a constant 

 temperature and of those which are unable to do so, 

 and these answer to the old warm-and cold-blooded 

 animals respectively. Those animals whose body- 

 temperature rises and falls as the temperature of 

 their environment rises and falls are now known as 

 poikilothermic, and those which are able to maintain 

 a constant temperature, however much the temper- 

 ature of the environment rises or falls, are known as 

 homoiothermic animals. This new classification 

 has been found necessar\- because of facts such as 

 the following : — The temperature inside a hive of 

 bees (and insects are classed as " cold-blooded) ma\- 

 even in winter time rise 2\° C. above that of the 

 outer air ; a mammal (a " warm-blooded " animal) 

 has, when hil>ernating, a temperature almost the 

 same as that of its cold environment : the tempera- 

 ture of a newl}--born mouse goes up and down w ith 

 that of its surroundings ; a frog or fish placed in 

 warm water becomes as warm as the water. In 



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