332 
DR. MARSHALL HALL ON HYBERNATION. 
rather compared to that state of the circulation which is observed in the frog 
from which the brain and spinal marrow have been removed by minute por- 
tions at distant intervals*. 
In fact, in the midst of a suspended respiration, and an impaired condition 
of some other functions, one vital property is augmented. This is the irri- 
tability, and especially the irritability of the left side of the heart. The left side 
of the heart, which is, in the hybernating animal, in its state of activity, as in 
all the other mammalia, only arterio-contractile, becomes veno-contractile. 
This phenomenon is one of the most remarkable presented to me in the whole 
animal kingdom. It forms the single exception to the most general rule, 
amongst animals which possess a double heart. It accounts for the possibility 
of immersion in water or a noxious gas, without drowning or asphyxia ; and it 
accounts for the possibility of a suspended respiration, without the feeling of 
oppression or pain, although sensation be unimpaired. It is, in a word, this 
peculiar phenomenon, which, conjoined with the peculiar effect of sleep in in- 
ducing diminished respiration in hybernating animals, constitutes the sus- 
ceptibility and capability of taking on the hybernating state. On the other 
hand, as the rapid circulation of a highly arterialized blood in the brain and 
spinal marrow of birds probably conduces to their activity, the slow circu- 
lation of a venous blood, doubtless contributes to the lethargy of the hyber- 
nating animal. 
6. Of the Digestion. 
There is much difference in the powers of digestion, and in the fact of omit- 
ting to take food, in the hybernation of different animals. The bat, being 
insectivorous, would awake in vain ; no food could be found : the hedgehog 
might obtain snails or worms, if the ground were not very hard from frost : 
the dormouse would find less difficulty in meeting with grain and fruits. We 
accordingly observe a remarkable difference in the habits of awaking from 
their lethargy or hybernation, in these different animals. 
I have observed no disposition to awake at all in the bat, except from ex- 
ternal warmth or excitement. If the temperature be about 40° or 45°, the 
hedgehog, on the other hand, awakes, after various intervals of two, three, or 
* Essay on the Circulation, pp. 13G — 141. 
