HEAT OF ANIMALS AND PLANTS. 261 



and in the whole substance of the Fungi (. 290.), and which 

 may be regarded as a sort of slow combustion. An evolution 

 of light has also been observed to take place, from dead and 

 decaying wood of various kinds, particularly that of roots ; and 

 also from Fungi whilst decomposing. This corresponds with the 

 luminousness of certain Animal bodies after death. 



407. It is well known that the higher Animals alone possess 

 the power, of keeping the temperature of their bodies up to a 

 certain fixed standard ; and that in the lower tribes, the heat of 

 the body varies with that of the atmosphere, being frequently 

 but a very little above it ; so that these, giving to the touch a 

 sensation of cold, are termed cold-blooded animals. Still, they 

 have some power of generating or producing heat, which is shown 

 by their power of resisting the influence of extreme cold for a 

 long time. In regard to Plants, much doubt has been enter- 

 tained at different times, whether they could be said to have a 

 proper heat or not ; or whether their temperature is not entirely 

 dependent upon that of the atmosphere. But this doubt has 

 resulted from a very limited view of the processes of the Vegetable 

 Economy, against which it is desirable to guard the young 

 reader. 



408. The production of heat in Animals is principally 

 dependent upon the conversion of Oxygen into Carbonic acid, by 

 its union with the carbon thrown off in respiration ; and just as 

 the rapid combustion of charcoal in oxygen gives out a great 

 degree of heat, so does the slower process of union in which the 

 respiration of human beings really consists, disengage heat more 

 gently. (ANIM. PHYSIOL. CHAP, vi.) Now in Plants this 

 process of respiration takes place so slowly (in comparison with 

 Animals), and from a surface so openly exposed to the atmo- 

 sphere, that it could scarcely be expected that there should be 

 any sensible elevation of the temperature of the part from th'S 

 source ; especially when it is considered that a constant loss of 

 heat is taking place by evaporation.* 



* See TREATISE ON HEAT. This fact is readily understood, by pouring a little 

 water, a little spirit of wine, and a little ether, one after another, upon the back 

 of the hand. Although they may have been all of the same temperature, the 



