256 ANIMAL HEAT. 



than the exterior. According to the experiments of Mr. Newport, 1 

 the interior of a hive of bees may have a temperature of 48.o. 

 when the external atmosphere is at 34.5, even while the insects 

 are quiet ; but if they be excited, by tapping on the outside of the 

 hive, it may rise to 102. In all cases, while the insect is at rest, 

 the temperature is very moderate ; but if kept in rapid motion in 

 a confined space, it may generate heat enough to affect the thermo- 

 meter sensibly, in the course of a few minutes. 



Even in vegetables a certain degree of heat-producing power is 

 occasionally manifest. Usually, the exposed surface of a plant is 

 so extensive in proportion to its mass, that whatever caloric may 

 be generated is too rapidly lost by radiation and evaporation, to be 

 appreciated by ordinary means. Under some circumstances, how- 

 ever, it may accumulate to such an extent as to become readily 

 perceptible. In the process of malting, for example, when a large 

 quantity of germinating grain is piled together in a mass, its ele- 

 vated temperature may be readily distinguished, both by the hand 

 and the thermometer. During the flowering process, also, an un- 

 usual evolution of heat takes place in plants. The flowers of the 

 geranium have been found to have a temperature of 87, while 

 that of the air was 81; and the thermometer, placed in the centre 

 of a clump of blossoms of arum cordifolium, has been seen to rise 

 to 111, and even 121, while the temperature of the external air 

 was only 66. 7 



Dutrochet has moreover found, by a series of very ingenious and 

 delicate experiment, 3 that nearly all parts of a living plant gene- 

 rate a certain amount of heat. The proper heat of the plant is 

 usually so rapidly dissipated by the continuous evaporation of its 

 fluids, that it is mostly imperceptible by ordinary means ; but if 

 this evaporation be prevented, by keeping the air charged with 

 watery vapor, the heat becomes sensible and can be appreciated by 

 a delicate thermometer. Dutrochet used for this purpose a thermo- 

 electric apparatus, so constructed that an elevation of temperature 

 of 1 F., in the substances examined, would produce a deviation in 

 the needle of nearly nine degrees. By this means he found that he 

 could appreciate, without difficulty, the proper temperature of the 

 plant. A certain amount of heat was constantly generated, during 



1 Carpenter's General and Comparative Physiology, Philadelphia, 1851, p. 852. 



2 Carpenter's Gen. and Comp. Physiology, p. 846. 



3 Annales des Sciences Naturelles, 2d series, xii. p. 277. 



