ON ANIMAL HEAT. 
559 
7. The temperature of the cold-blooded vertebrata is generally 
low, and that of the amphibia and reptiles only a degree or two 
higher than the surrounding medium. This is not always the 
case, for in tropical countries the land-tortoises maintain a tem- 
perature considerably less than that of the atmosphere. “The 
temperature of the air of the Gallipagos Islands varies from 72® to 
75° ; that of the blood of the tortoise is always 62°.” (Porter's 
Journal, p. 215.) Fishes usually support an internal heat slightly 
superior to the temperature of the water they live in. Some ex- 
ceptions, however, have been discovered. Dr. Davy found that 
the thunny ( thynnus pelamys) possessed a heat of 99°, when the 
surrounding water was only 80^° Fahr. 
8. Insects develop a degree of heat governed mostly by the 
temperature of the medium in which they move. Mr. Newport, 
in his experiments on them, was always able to detect an inde- 
pendent temperature, which in some cases exceeded that of the 
atmosphere by 20®. When quantities of them associate together, 
the heat produced is considerable. J. Hunter placed a thermo- 
meter in a bee-hive, and ascertained that the temperature varied 
in spring from 93° to 98°, and in the summer it reached as high 
as 104o. 
9. Plants give satisfactory evidence of the possession of a 
temperature independent of external circumstances. When snow 
falls on plants, the first part which melts is that immediately in- 
vesting the leaf. On inserting the bulb of a thermometer into a 
hole cut in a tree, the mercury invariably rises beyond that of the 
external air. 
10. The use of the mercurial thermometer for measuring slight 
variations in the temperature of the animal, or of its different 
component parts, is not without a great liability to error. It is 
very difficult of application to the internal organs, without detri- 
ment to the experiment, and in many instances objectionable, 
from the impossibility of its being affected unless it obviously ab- 
stracts a proportion of caloric from the tissue to which it is ap- 
plied. On this account the experiments of MM. Becquerel and 
Breschet, who employed, in their investigations on the subject of 
animal heat, the thermo-electric multiplier, which is free from 
the sources of error affecting the common thermometer, are worthy 
of the firmest reliance. 
11. Most writers on animal caloric agree that the tempera- 
ture of the foetus is supplied wholly by the mother. This rests 
altogether on supposition. There is, however, some reason to 
doubt the' correctness of it, from the fact of the cold sensation 
experienced by the parent on the occurrence of inter-uterine death. 
12. It is asserted by Dr. Edwards, and by Despretz, that the 
