

CHAPTER XXIV. 



ANIMAL HEAT. 



PART of the work done or energy set free by the chemical 

 changes in the animal tissues appears as heat which is devoted to 

 keeping the body warm ; for the bodies of most animals are con- 

 siderably warmer than their surroundings. Warm-blooded ani- 

 mals are those which habitually preserve an even temperature 

 independent of the changes which take place in that of the medium 

 in which they live ; and as the term warm-blooded implies, their 

 temperature is, as a rule, higher than the surrounding air or 

 water. Cold-blooded animals, on the other hand, are those whose 

 temperature is considerably affected by, or more or less closely 

 follows, that of the medium surrounding them. 



The blood of all mammalia has pretty much the same tempera- 

 ture as that of man, about 37.5 C., and probably varies under 

 similar circumstances. But birds, the other class of warm-blooded 

 animals, have a temperature about 4 or 6 C. higher than that 

 of mammals. 



The blood of those animals whose temperature follows the 

 changes that occur around them, is generally from 1 to 5 C. 

 higher than the medium in which they live. They produce some 

 heat, though it be in small quantity, and since they have no special 

 plan for its regulation, it does not remain at a certain standard. 

 Wherever active oxidization takes place, heat is produced ; so 

 even in invertebrate animals an elevation of temperature occurs; 

 this can be easily ascertained when they exist in masses, as bees, 

 an active hive sometimes reaching a temperature of 35 C. 



Instead of the term " warm-blooded," it is more accurate to 

 apply to animals whose temperature remains uniformly even, and 

 independent of their surroundings, the term " Homceothermic " 



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