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 tremellee, 
or the hard stony substance of the commen coral (Coralli- 
na polymorpha), from the gelatinous and transparent me- 
duse. 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.—T he two circumstances which we have 
already pointed out as necessary to the commencement and 
continuance of the vital functions, are nevertheless insufli- 
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 durmg 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. Wife is likewise destroyed by a tempera- 
