622 



EVOLUTION OF HEAT, LIGHT, AND ELECTRICITY. 



so that it is scarcely possible to entertain a reasonable doubt, that the produc- 

 tion of Heat in Plants is dependent upon a process of slow combustion. When 

 the general phenomena of Calorification in Animals are carefully examined, 

 they are found to harmonize with this view. Throughout the whole kingdom, 

 a close and exact conformity may be perceived between the amount of Oxygen 

 consumed and of Carbonic acid given off, and the degree of Heat liberated. In 

 the cold-blooded animals, whose temperature is almost entirely dependent upon 

 that of the surrounding element, the respiration is feeble ; being carried on, for 

 the most part, through the medium of water. In the warm-blooded Vertebrata, 

 however, which have the power of keeping up the heat of their bodies to an ele- 

 vated standard, even when that of the surrounding air is far beneath it, the 

 quantity of oxygen consumed is very large ; and that required by Birds is more, 

 in proportion to their size, than that employed by Mammalia, as we should ex- 

 pect from the more elevated temperature of the former. In the class of Insects, 

 we have a very remarkable illustration of the same general fact. It appears, 

 from the researches of Mr. Newport, 1 that Insects, during their larva and pupa 

 states, and even in their perfect condition when at rest, are to be regarded as 

 truly cold-blooded animals ; their temperature rising and falling with that of 

 the surrounding medium, and being at no time more than a degree or two above 

 it. In a state of activity, however, the temperature of the body attains a con- 

 siderable elevation ; frequently as much as 10 or 15 above that of the air. It 

 must be remembered that, owing to their larger extent of surface in proportion 

 to their bulk, small animals are cooled much more rapidly than large ones ; and 

 the temperature of insects would probably rise much higher, if it were not 

 for the loss they are thus continually experiencing, which is greatly increased 

 by the action of the wings. In one of Mr. N/s experiments, a single Humble- 

 bee, in a state of violent excitement, communicated to three cubic inches of air 

 as much as 4 of heat within five minutes ; its own temperature being raised 7 

 in the same time. When several individuals in a state of excitement, however, 

 are clustered together, so that the loss of heat is prevented, the elevation of 

 temperature is much more considerable; thus, a thermometer introduced among 

 seven " nursing-bees" stood at 92 , whilst the external air was only 70; and 

 the temperature of a hive was raised by disturbing it, during winter, from 48 

 to 102, the temperature of the air being only 34 at the time. In all these 

 instances, the amount of Oxygen consumed bears an exact proportion to that of 

 the Heat evolved. 



these spadixes, hour by hour, during the "paroxysm" of flowering, and the quantity of 

 oxygen consumed during the same periods, with the following result; the amount of heat 

 developed being expressed by the number of degrees (Cent.) shown by the thermometer 

 above the temperature of the surrounding air, and the quantity of oxygen consumed being 

 stated in multiples of the volume of each spadix. 



1 "Philosophical Transactions," 1837. 



