THE HETEROTHERMOUS CONDITION OF THE 

 TISSUES OF WARM-BLOODED ANIMALS 



Laurence Irving 



Appreciation for the universality of physical laws Degan to de- 

 velop toward the close of the eighteenth century as the metabolic 

 production of animal heat was ascribed to combustion. Lavoisier 

 (1777) estimated that the heat caused by formation of the carbon di- 

 oxide expired by a rabbit was nearly equivalentto the heat which the 

 animal gave off to a calorimeter, and he confidently attributed the 

 production of heat by animals to processes of oxidation. 



In 1840 Julius RobertMayer, a young physician in Java, followed 

 the then prevailing custom of bleeding sailors as they arrived in a 

 tropical port. When he observed that the venous blood appeared ar- 

 terial red he consulted with a colleague and was informed that in 

 Java venous blood appeared arterial in color. His imagination led 

 him to think that the diminished need for metabolic heat in a tropi- 

 cal climate brought about less reduction of oxygen in the venous 

 blood than was usual in a colder climate. Reflecting upon this dubious 

 explanation, he was led to produce comprehensive physiological and 

 astronomical illustrations of the transformation of energy, from 

 which he developed the general view of the conservation of energy 

 (Tyndall, 1898). Mayer's explanation of the color of venous blood 

 does not sound valid, however, for people in warm and cold climates 

 have about the same basal production of heat, adjusting the elimina- 

 tion of heat to the climate by varying the circulation and temperature 

 in their skin. 



ARCTIC CLIMATE 



Cold northern climates are advantageous for studying thermal 

 reactions of animals because the winter weather is so much cokier 

 than the bodies of warm-blooded animals. Over the northern interior 

 of Asia and America extreme seasonal changes occur. At Allakaket 



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