PERIODICAL BIRDS TO BECOME TORPID. 109 
very many White Martins (Hirundo urbica) ; they 
also congregated and died, lying ten and twelve deep 
on the different window-sills. 
“The manner in which they congregated was a 
curious feature in the occurrence. A Swallow would. 
fly round a heap of dead and dying companions, 
and then suddenly dart down and bury itself among 
them.” 
How the well-known fact that the Periodical 
Summer Birds which appear in this country in 
spring uniformly bear only a small proportion to 
those that withdraw from observation in autumn is 
to be satisfactorily explained on the supposition that 
the birds in question pass the cold season in a 
state of torpidity, the ingenuity of those persons 
who advocate the hypothesis of hybernation must 
determine. 
The effects produced by variations in tempera- 
ture upon the Dormouse (Myoxus avellanarius) 
and other animals whose liability to become tor- 
pid is unquestionable, claim attention in the next 
place. 
Having obtained five healthy Dormice, I endea- 
voured, at various periods in the year 1824, to 
render them torpid by the employment of artifi- 
cial means. Two of them were placed in a tall 
cylindrical glass jar, with a supply of flax and 
cotton for the construction of a dormitory; and 
when they were familiar with their new residence, 
