PERIODICAL BIRDS TO BECOME TORPID. 113 
and Iam disposed to think that the legitimate in- 
ference to be deduced from the facts is, as I have 
already stated, that birds have no tendency whatever 
to torpidity, which seems to result from diminished 
nervous uritability, occasioned by a low degree of 
temperature, more or less directly affecting numerous 
important vital functions, as circulation, respiration 
(and necessarily the evolution of animal heat), 
digestion, secretion, assimilation, absorption, and ex- 
cretion. 
That the Periodical Birds which visit this country 
in autumn are not rendered torpid by cold, will be 
readily acknowledged, as they are known to quit the 
north of Europe on the approach of winter for more 
genial climates in lower latitudes; and it has been 
shown that even in Britain the Redwing frequently 
falls a victim to severe and protracted frosts. Why, 
then, should any reluctance be felt to admit that the 
Periodical Birds, whose appearance in spring is at- 
tended with so many pleasing associations, retire 
from this kingdom on the return of the cold season 
to more southern countries, where a suitable tem- 
perature and an ample supply of food are to be 
found? I have endeavoured to prove by experiment 
that they do not become torpid; and I may add that 
a premium of five pounds a head, publicly offered for 
birds in a state of perfect torpidity, when I resided 
at Crumpsall Hall, failed to produce a single indivi- 
dual, though, for a fifth part of the sum, I know that 
I 
