136 



ANIMAL. 



one of the products of the laws of vitality with 

 the essence of which we are altogether un- 

 acquainted. 



Besides the secretion of the various gaseous, 

 fluid and solid matters mentioned, vegetables 

 and animals appear in common to possess the 

 power of disengaging certain imponderable 

 elements heat, light, and electricity. 



Heat. There has been considerable variety 

 of opinion among physiologists with regard to 

 the extent to which vegetables have the power 

 of maintaining a temperature of their own inde- 

 pendently of that of the surrounding media. 

 Nor is this question, in our opinion, yet com- 

 pletely set at rest. It is certain that trees in 

 high northern latitudes endure a cold many de- 

 grees below zero without injury, whilst in in- 

 tertropical countries they are frequently ex- 

 posed even in the shade to a heat above that 

 of any animal without perishing; actual ex- 

 periment, indeed, proves that they preserve a 

 temperature intermediate between that of the 

 extreme heat and extreme cold of the diurnal 

 variations of those latitudes in which they are 

 indigenous. This circumstance is explained 

 variously, some attributing it to a vital property 

 in plants to regulate to a certain extent their 

 own temperature, others alleging that it is 

 merely owing to the indifferent conducting 

 qualities of the materials of which vegetables 

 are composed. The thermometer has been seen 

 several degrees below the freezing point of 

 water within the trunks of fir trees, without 

 their vitality being affected ; but it is probable 

 that the constitution of this tribe renders them 

 capable of enduring such a reduction of tem- 

 perature with impunity as would prove fatal to 

 other trees with simple watery sap. 



On the other hand, it is quite certain that the 

 flowers of many vegetables have the power of 

 disengaging heat, a difference of ten, twenty, 

 and even more than thirty degrees having been 

 observed at sun-rise between the temperature 

 of the atmosphere and that of the flowers of 

 different vegetables in southern latitudes, and 

 the same thing is known to occur, though to a 

 less extent, in northern countries. 



It would therefore be unfair, with such facts 

 before us, to deny altogether to vegetables the 

 faculty of disengaging caloric. Arguments, in- 

 deed, a priori, might be adduced to show that 

 they must almost necessarily possess such a 

 property : they are the subjects of incessant 

 change ; and one of the most universal of the 

 physical laws involves a change of temperature 

 on any change of constitution. 



If the faculty of vegetables generally to 

 secrete or eliminate caloric be doubtful, how- 

 ever, it is indisputable that among all animals 

 a little raised above those at the very bottom of 

 the scale, there is an inherent power of gene- 

 rating caloric, which in their state of maturity 

 is nearly determinate as regards each particular 

 species.' Mammalia and birds have universally 

 the highest temperatures. 



Reptiles or cold-blooded animals, as they 

 are improperly called, have also the power of 



engendering heat, and of regulating their own 

 temperature : this faculty, however, and the 

 degree of heat they possess at different times, 

 are influenced to a very considerable degree by 

 the heat of the media in which they live. The 

 same statements may be made with regard to 

 fishes. The temperature of these creatures is 

 generally several degrees above that of the water 

 they inhabit; but it also varies with the tem- 

 perature of their native element. 



Many insects have a very decided power of 

 engendering heat and of regulating their tem- 

 perature ; and similar faculties have been de- 

 monstrated in the Crustacea, the mollusca, and 

 the annelida. These tribes, however, are all 

 very much influenced by the temperature of the 

 media surrounded by which they live. 



No great difference is therefore discernible 

 between vegetables and animals in the faculties 

 they possess of engendering caloric and regu- 

 lating their own temperature; the faculty is 

 only much more decided, and possessed to a 

 far greater extent among the more perfect 

 classes of animals generally than among vege- 

 tables at large. It may very fairly, in the 

 present state of our knowledge, be ascribed as 

 a common property. 



As to the mode in which heat is engendered, 

 opinions are still very much divided. The 

 chemical and mechanical explanations that 

 have been given of the phenomenon are not 

 universally applicable. All we can say at the 

 present day is that the production of heat and 

 the power of regulating their temperature pos- 

 sessed by organized beings is another of the 

 hidden and singular laws or properties intro- 

 duced into the system of the universe with their 

 creation. 



Light. Many unorganized bodies have the 

 property of shining or giving out light for some 

 time after they have been exposed to the bright 

 rays of the sun, or have been heated in the fire, 

 or when they are struck together or smartly 

 compressed, and this certainly without any 

 decomposition of their substance. The disen- 

 gagement of light, again, is a very uniform 

 accompaniment of the decomposition and com- 

 position of inorganic substances, and it appears 

 to be a very constant attendant upon electrical 

 phenomena. 



Various organic substances and products of 

 organization have a similar property; living 

 vegetables, too, particularly the flowers, have 

 been seen to give out light by authorities so 

 respectable, that though the fact has been 

 called in question by others of great name, 

 there seems no sufficient reason for treating all 

 that has been said on the subject as illusion : 

 in the physical sciences negatives cannot be 

 received as evidence of equal value with posi- 

 tives. 



No one thinks of calling in question the 

 luminousness of animals ; most of the innu- 

 merable inferior tribes that live in the sea, 

 appear to possess and to manifest this pro- 

 perty at different seasons. The luminous- 

 ness of the ocean itself, so familiarly known, 

 seems to depend on the presence of multitudes 



