794 ANIMAL HEAT. 



A consideration of the above lists shows that the temperature of cold- 

 blooded animals is generally a few tenths of a degree above that of their 

 surroundings, but that in some exceptional cases, as that of the python and 

 a fish known as the bonito (Thynnus pelamys), it may be 10 degrees 

 above the external temperature. Although these high temperatures are well 

 authenticated, the causes have not been determined ; it is to be noted, how- 

 ever, that the high temperature is more marked in the incubating female 

 python than in the male which does not incubate, and that the bonito has very 

 vascular red muscles. 1 



The temperature of many of the cold-blooded animals is often below 

 that of the air, owing to the great loss of heat by evaporation, and to 

 the large surface exposed, especially by insects, to cooling by radiation and 

 conduction. 



Hibernation. 2 Certain animals, on the approach of winter, and in some 

 cases even in summer, retire to their burrows or other shelter, become inactive, 

 and fall into a torpid state. All the activities of the body are greatly reduced, 

 and the temperature falls to a point only slightly above that of the surround- 

 ings. Such is the condition known as hibernation. 



The animals in whom hibernation has been definitely proved to take 

 place, do not belong to any one class ; examples are met with in mammals, 

 reptiles, amphibians, insects, 3 molluscs, and lower animals, but no cases 

 are known among birds. As regards fishes, no well-authenticated cases of 

 hibernation are known ; there are doubtful instances in which the fish has 

 been imprisoned by the freezing of the water, and yet has remained alive for 

 some time. 



The following mammals hibernate spermophile, marmot, hamster, 

 squirrel, hedgehog, dormouse, bat, bear, and beaver. In some cases the 

 animal lays up stores of food, upon which it feeds when it awakes at 

 intervals during the period of hibernation ; in other cases, there is a special 

 accumulation of fat within the animal's body before the commencement of the 

 torpid state. 



The further account of this subject refers only to the hibernating 

 mammals. 



The condition of the animal during hibernation. Respiration. The 

 frequency of respiration is greatly diminished, and the rhythm is irregular 

 and often of the Cheyne-Stokes type. A hibernating dormouse may not give 

 a single respiration for ten minutes, then may take ten or fifteen breaths, and 

 again cease breathing for another period of several minutes. The same animal 

 in an active condition breathes at the rate of eighty or more in a minute. 

 Similar results have been obtained in the case of other animals. 



Determinations of the respiratory exchange have been made. Spallanzani 4 

 found that during hibernation marmots and bats could be kept for four hours in 

 carbon dioxide gas without suffering any ill effects, whereas a bird and a rat 

 placed in the chamber at the same time died at once. Saissy 5 observed that 

 the amount of oxygen taken up by dormice varied as the activity of the 

 animal, and that during well-marked hibernation there was hardly any intake. 



1 See p. 849. 



2 Since this section was written, there has appeared a monograph by Dubois, " Physio- 

 logic compared de la marmotte," Paris, 1896, which contains a large number of original 

 observations and an abstract of the previous work upon hibernation. The bibliographical 

 index contains references to 145 papers. 



3 Trimen, "Butterflies of South Africa," vol. i. p. 231. See also Nature, London, 2nd 

 April and llth June 1896. 



4 Spallanzani, "Memoirs on Respiration," edited by Senebier, 1804. See article 

 "Chemistry of Respiration," this Text-book, vol. i. 



5 "Recherches experimentales anatomiques, chimiques," etc., 1808; Reeve, f '0n 

 Torpidity," 1809; Edwards, " De I'influence des agens physiques sur la vie," Paris, 

 1824. 



