DR. MARSHALL HALL ON HYBERNATION. 
355 
When we read of insensibility, of a stiffened state of the muscles, and of a 
cessation of the circulation, as obtaining in hybernation, we may be certain 
that a state of torpor has been mistaken for that condition. The actually 
hybernating animal exposed to continued severe cold, is, as M. Saissy correctly 
observes, first roused from this state of ease and preservation, into a painful 
activity, and then plunged into a fatal torpor. 
This subject will come to be considered in a subsequent part of this inquiry, 
in which I purpose to trace the effects of cold in changing the relative quan- 
tity of respiration and degree of the irritability in animals of different ages 
which do not hybernate ; in the meantime, the accurate distinction between 
mere torpor, which may occur in any animal, and which is a destructive state, 
from true hybernation, which is preservative, and the peculiarity of certain 
animals, will enable us to correct many inaccuracies into which Legallois*, 
M. Edwards -j-, and other physiologists have fallen. 
IV. Of Reviviscence. 
Not the least interesting of the phenomena connected with hybernation, are 
those of reviviscence. Hybernation induces a state of irritability of the 
left side of the heart, which, with high respiration and an arterialized blood, 
would be incompatible with life. Respiration suddenly restored, and perma- 
nently excited, is, therefore, as destructive as its privation in other circum- 
stances. 
All those bats which were sent to me from distant parts of the country died. 
The continued excitement from the motion of the coach, keeping them in a 
state of respiration, the animal perished. One bat had, on its arrival, been 
roused so as to fly about. Being left quiet, it relapsed into a state of hyber- 
nation. The excitement being again repeated the next day, it again flew about 
the room ; on the succeeding day it w r as found dead. 
It is in accordance with this law, that we observe hybernating animals 
adopting various measures to secure themselves from frequent sources of dis- 
turbance and excitement. They choose sheltered situations, as caverns, bur- 
rows, &c., secure from the rapid changes and the inclemencies of the weather 
* (Euvres de Legallois : Paris, 1824, p. 282. f Agens Physiques, pp. 292, 148. 
