494 THE BLOOD. 



The temperature of animals is very equal throughout the 

 body, the surface being cooler than the interior, and the in- 

 ternal heat being little influenced by the temperature of the 

 external air. Dr Davy found the heat of the human body 

 a little increased in the torrid zone. Sir George Back 

 ascertained the temperature of foxes in the arctic regions to 

 be the same as that of our British ones. Disease affects the 

 heat of the body; we find it raised to 1.07 in fever, and as 

 low as 80 in cyanosis. 



The great source of animal heat is the oxidation of mate- 

 rials in the body. Mayo first held this opinion, and Black 

 and Lavoisier afterwards indicated that the development of 

 animal heat was connected with the respiratory process. 

 These authors believed the heat to be generated in the lungs, 

 but a difficulty arose as to how it could be explained that 

 the lungs were not hotter than other parts of the body. 

 Crawford attempted an explanation, on the ground that diffe- 

 rent substances have a different capacity for heat, and that 

 arterial blood had a larger capacity for heat than venous. 

 The rapidity of the blood's flow would have accounted 

 for the diffusion of heat, but La Grange and Hassen- 

 fratz superseded the views entertained by Black and 

 Lavoisier, and suggested that heat was produced throughout 

 the whole body. There is no doubt a singular relation 

 between the activity of the respiratory act and the tempera- 

 ture of the body. This is especially noticed in comparing 

 the activity of respiration and the temperature between birds 

 and mammals. In puppies, the ductus arteriosus keeps 

 open until the eyes open, and during this period respiration 

 and the production of animal heat are below par. In hyber- 

 nating animals, it is observed that respiration is active in 

 summer and the temperature of the body high; in winter, 

 breathing is almost entirely suspended, and the body cools 



