os , 
.* 
414 TORPIDITY. 
bernating period, some of them possessing the power 
of voluntarily resisting it, and others waiting the 
arrival of a cerlain amount or measure of that 
influence which in them induces it. It is not caused 
in all hybernating animals by only one, or even 
perhaps by only two circumstances external to 
them. Is perhaps invariably preceded by some 
remarkable instincts and reasoning processes, se- 
curing the subjects of it from many inconveniences, 
and ledentia which might else obtain during the 
torpid state. Does not of necessity affect every in- 
dividual of a hybernating species. Its duration in 
different animals (and its interruptions when such 
occur) is apparently always determined by the 
state or amount of that influence which caused it. 
May be suspended by artificial means,—but does 
not seem conformable in all times and cases to the 
presence or absence ofits very exciting cause. Is 
in many instances capable of being induced by ar- 
tificial means at unnatural seasons, and by accumu- 
lation of the amount of its probable cause may be 
brought about in the individuals of many species 
which happened not to have been affected by it at 
the natural time. Is perhaps capable of being 
induced in species never habitually its subjects by 
great concentration of some exciting cause. Its 
intensity varies greatly in species, in individuals of 
a species, and is not uniform in all seasons in any 
kind. 
Tortoises.—Decidedly the most instructive exam- 
ple of the tendency to torpidity occurs in tortoises 
as we see them in this climate, several degrees colder 
than their natural homes. All the individuals whose 
habits I have received information of, shew a degree 
of sensitiveness to the amount of cold deciding 
their torpidity and revival which is altogether be- 
yond our comprehension, and may be termed in truth 
exquisite. In the first place, the period when they 
