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. S49. 
2 Since this section was written, there has appeared a monograph by Dubois, " Physio- 
logie comparee de la mannotte," 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 Xature, London, 2nd 
April and 11th June 1896. 
4 Spallanzani, "Memoirs on Respiration," edited by Senebier, 1S04. See article 
"Chemistry of Respiration," this Text-book, vol. i. 
5 "Recherches experimentales anatomiques, ehimiques," etc., 1808; Reeve, "On 
Torpidity," 1809 ; Edwards, " De l'influence des agens physiques sur la vie," Paris, 
1824. 
