7 88 ANIMAL HEAT. 
a higher temperature than that of most cold-blooded animals, and are 
not reduced to spend the winter in a torpid state. 
Even in the case of the most perfectly warm-blooded animals there is 
a stage in which they resemble cold-blooded animals ; infants and young 
animals born in an immature condition cannot maintain the temperature 
of their bodies at the normal height of the temperature of the adult ; 
they need some accessory source of heat, such as the warmth of the 
parent's body. 
The terms " warm-blooded " and " cold-blooded " are inexact, for the tem- 
perature of a so-called cold-blooded animal living in the tropics may, under 
some circumstances, equal that of a mammal. John Hunter 1 showed that 
the essential difference in the two classes was in the constancy and incon- 
stancy of the temperature of the two groups, and he suggested that the warm- 
blooded animals should be called "animals of a permanent heat in all atmo- 
spheres;" the cold-blooded, "animals of a heat variable with every atmosphere." 
Again, in 1845, Donders' 2 pointed out the same fact, and called the two groups 
of animals, those with a constant and those with an inconstant temperature. 
A year or two later, Bergmann 3 discussed very fully the objections to the 
old terms, and suggested the definitions, " animals with a constant temperature 
and animals with a varying temperature, or homoiotliermic and poikilothermic 
animals." In the present article, however, the terms "warm-blooded" and 
"cold-blooded" are retained, for they have been sanctioned by long usage, and 
their meaning is well understood. A further reason for their retention is 
found in the fact that there is no hard-and-fast line between the animals with 
a constant temperature and those with a varying temperature. 
The temperature of man and other warm-blooded animals. — 
The temperature of man. — The mean daily temperature of a healthy 
man varies slightly according to the part of the body in which it is 
observed: in the rectum it is 37°*2 (98 0, 96 F.), in the axilla 36 0- 9 
(98°-45 F.), in the mouth 36°-87 (98°-36 F.). These figures are the 
averages selected from the different observations given in the table on 
p. 789, and represent the mean temperature of a working day. 
The normal temperature of man is generally stated, as the result 
of John Davy's numerous observations, to be 36°*9 (98 0, 4 F.) in the mouth. 
This, however, is wrongly looked upon as the mean temperature of 
twenty-four hours, for it represents the mean of observations taken 
chiefly during the active part of a day, from about 8 a.m. to 12 o'clock 
midnight ; all observers agree that the lowest temperatures are found 
between midnight and early morning, and for very evident reasons the 
observations during this period are few. The mean temperature of 
twenty-four hours is therefore without doubt below 36°-9 (98 0, 4 F.), and 
the observations of Casey, Clifford Allbutt, and Ogle show that this 
figure is even too high for the mean temperature of a working day. 
The average obtained from their results is 36°'7 (98 0, 14 F.) for the 
temperature taken in the mouth. The observations upon the tem- 
perature between midnight and morning are so few, that it is im- 
possible at present to give the mean temperature of a day of twenty-four 
hours. 
1 "Works," Palmer's edition, London, 1837, vol. iii. p. 16. 
- "Der Stoffwechsel als die Quelle der Eigenwarme bei Pflanzen and Tbieren," Wies- 
baden, 1847, S. 12-13. 
3 "Gottinger Studien," 1847, Abtb. 1, S. 595. 
