30 PHILOSOPHY OF ZOOLOGY. 



of the vital principle being retained by the solids after ab- 

 solute desiccation. 



The quantity of fluids necessary to the exercise of the 

 functions of organized bodies is very various, according to 

 the species. How different the dry powdery appearance 

 of many of the lichens, compared with the watery tremellae, 

 or the hard stony substance of the common coral (Coralli- 

 na polymorpha), from the gelatinous and transparent me- 

 dusae. In all cases, the quantity of fluid is greatest du- 

 ring the period of growth, and decreases beyond the term 

 of maturity. Hence the plumpness and flexibility of 

 youth, the aridity and stiffness of age. 



3. Temperature. The two circumstances which we have 

 already pointed out as necessary to the commencement and 

 continuance of the vital functions, are nevertheless insuffi- 

 cient for the purpose, without the aid of a suitable tempera- 

 ture. Unless supplied with heat, the seeds of plants do 

 not germinate ; and the eggs of animals are not hatched. 

 Even after the commencement of the living action, anima- 

 tion is suspended or destroyed, when the temperature sinks 

 below a certain degree, which differs according to the spe- 

 cies. In some animals, reviviscence and torpidity may be 

 produced by turns, by the communication or abstraction of 

 caloric. 



In many cases, where an elevated temperature^ or one 

 higher than the surrounding medium is required, as in 

 some plants during the fecundation of the seed, and in 

 warm blooded animals, organs are provided which occasion 

 the evolution of caloric ; and, when this fluid ceases to be 

 produced, the functions of life are suspended or destroyed. 

 In general, when the temperature descends to the freezing 

 point, animation is either totally destroyed or suspended ; 

 and, below that temperature, circulation ceases, and the 

 fluids congeal. Life is likewise destroyed by a tempera- 



