TEMPERATURE OF ANIMALS. 873 



than their own bodies. Moreover, each kind of animal is able to main- 

 tain, within a certain range, a temperature proper to itself; but, since 

 even living animals, like dead ones and inorganic bodies, exhibit the 

 same physical phenomena of absorption, conduction, and radiation of 

 heat, they undergo constant changes, usually in the direction of a loss 

 of heat. Hence, there must exist within them a power of constant 

 renewal, or production, of fresh heat. The standard temperature of 

 an animal is understood to express its proper heat; whilst the form of 

 heat produced in its body, for the maintenance of this temperature, is 

 known as Animal Heat. 



This function of producing heat is universal in the Animal Kingdom, and 

 all the processes of animal life are influenced by it. 



Animals have been divided, according to their temperature, into the Cold- 

 blooded and the Warm-blooded animals, the former being understood to include 

 all the Non-vertebrate animals, and, amongst the Vertebrata, the Fishes, 

 Amphibia, and Keptiles ; whilst the Warm-blooded animals consist of the 

 Birds and Mammalia, including Man. Amongst the Non-vertebrate Classes, 

 the Protozoa and Coelenterata, having no proper blood system, can hardly be 

 designated cold-blooded ; yet they have a close relationship, as regards the 

 phenomena of temperature, with that division of animals. It has been pro- 

 posed to name the Cold-blooded animals, animals of variable temperature, and 

 the Warm-blooded creatures, animals of constant temperature; because the for- 

 mer have their actual temperature greatly influenced by, that is to say, elevated 

 or lowered, according to corresponding changes in the temperature of the media 

 in which they live ; whilst, on the other hand, the latter exhibit nearly a uni- 

 form temperature, under important alterations in that of the surrounding 

 media. (Bergmann.) 



In regard to the Protozoa, it has been shown, that when water containing 

 Infusoria, is frozen, these minute creatures are not always necessarily de- 

 stroyed by being likewise frozen, but each survives for a certain time, sur- 

 rounded by a little uncongealed watery space ; this can only be accounted for, 

 on the supposition that the animalcule continues to produce a minute quantity 

 of proper or individual heat. In the aquatic N on- vertebrate animals generally, 

 a similar power of resisting cold exists ; though there are but few observations 

 on the heat-producing powers of these animals. The temperature of a number 

 of earth-worms, leeches, slugs, or snails, collected in heaps, has been found to 

 be from 1 to 2 higher than the air. In the air-breathing Insects, the heat 

 evolved in the larval or caterpillar stage, is sufficient to maintain the body 

 from to 2 in the Lepidoptera, and from 2 to 4 in the Hymenoptera,. 

 above that of the surrounding medium. In the chrysalis stage, the tempera- 

 ture is nearly that of the surrounding medium, very' little heat being evolved. 

 In the perfect Insect, the temperature may vary in the bee from 3 to 10, 

 and in the butterflies from 5 to 9, above that of the air. The temperature 

 of bees, in numbers, as in a hive, may be as high as 16 above that of the air. 

 The nursing bees sometimes reach a temperature of 22^ above that of the 

 atmosphere. Insects, therefore, under certain circumstances possess a heat- 

 producing power nearly equal to that of the warm-blooded animals. The tem- 

 perature of bees is raised by exercise and excitement, and diminished by rest, 

 sleep, hibernation, and want of food. 



In Fishes, the temperature of the blood is usually from to 1 warmer 

 than the surrounding water at mean temperatures. In other instances, it is 

 2 to 3 higher, and in a few exceptional cases, in which the muscles and the 

 blood are darker, the heart is larger, and the gills provided with enormous- 

 nerves, as in the tunny and bonito, the temperature is still higher ; that of 

 the bonito has been found to be 99, or 18 above the temperature of the sea, 

 (Davy. ) In the frog, when the external medium has a temperature of about 

 60, the animal is from | to 1| warmer than it ; but when the external tern- 



