RESPIRATION 211 



46. Animal Heat. Intimately connected with respiration is 

 the production of animal heat, or the power of maintaining the 

 temperature of the body above that of the medium in which 

 the creature moves ; thus, the bird is warmer than the air, and 

 the fish than the water. This elevation of temperature is the 

 result of the various chemical changes which are constantly 

 taking place in the system. Although common to all animals, 

 in a greater or less degree^heat is not peculiar to them, since 

 plants also generate it, especially at the time of sprouting and 

 flowering. If a thermometer be placed in a cluster of geranium 

 flowers, it will indicate a temperature several degrees above 

 that of the surrounding air. 



47. Among animals great differences are noticed in this 

 respect, but the degree of heat produced is always proportional 

 to the activity of respiration and the amount of oxygen con- 

 sumed. Accordingly, the birds, whose habits are extremely 

 active, and whoss breathing capacity is the greatest, have uni- 

 formly the highest temperature. Sluggish animals, on the 

 contrary, as frogs, lizards, and snakes, have little need for 

 oxygen, and have incompletely developed lungs ; these animals 

 are cold to the touch that is, they have relatively a lower 

 temperature than man, and their positive temperature is but 

 little above that of the external air. Accordingly, zoologists 

 have so arranged the animal kingdom that warm-blooded ani- 

 mals, including man, the birds, and the quadrupeds, are classi- 

 fied together ; while the coldblooded animals, such as the fish, 

 tortoise, frog, and all that have no vertebral column, are classed 

 by themselves. 



again from our houses even once in an hour, is a process which cannot be 

 accomplished without paying roundly ; yet on no other condition can we 

 reasonably expect health and long life. The best way is to freely admit 

 that it is expensive, but worth the money it costs. If Benjamin Franklin 

 thought that 'a penny saved is a penny earned,' he is equally sure that 

 4 health is wealth.' " George Derby on the Prevention of Disease. 



46. Warmth of the bird as compared with that of the air ? Of the fish and the water ? 

 Heat in animals and plants ? How illustrated with the thermometer ? 



47. Amount of heat in animals, how apportioned f As regards the birds ? Frogs, and 

 other sluggish animals ? Arrangement made by zoologists ? 



