282 FACULTIES OP BIRDS. 



ter, but remain in the island, and issue from their 

 retreat in warm days in quest of food.* 



As the dormouse, the bat, and other hybernating 

 animals do not appear to have any peculiarity of 

 anatomical structure from which we might account 

 for the circumstance, besides certain depositions of 

 fat and a valvular conformation of the veins, the 

 use of which is not well known, we cannot, conse- 

 quently, make any inference upon this point from 

 the anatomical structure of swallows and other mi- 

 gratory birds. But experiment is no less valuable 

 a test than structure, and experiments respecting 

 the conjectured torpidity of the swallow were tried 

 by Spallanzani, who found that swallows do not ap- 

 pear to suffer by cold at the freezing point ; while 

 at eight or nine degrees below it they manifest un- 

 easiness, and at thirteen or fourteen degrees below 

 it they speedily perish. In order to discover the 

 effect of a continued low temperature, Spallanzani 

 confined some swallows in wicker cases covered 

 with waxed silk to keep them dry, burying them in 

 snow, with only a hole to admit air. After having 

 been immersed for thirty-five hours, some of them 

 were dead, and others exhibited signs of great 

 weakness, but without any appearance of torpidity 

 or even lethargy ; in ten hours more they were all 

 found dead. That they had not died in consequence 

 of want of food, he further proved by keeping other 

 swallows without food in his study, when he found 

 they could support life from three to five days with- 

 out anything to eat. 



A still more convincing proof that swallows do 

 not become torpid in winter, may be derived from 

 those which have been successfully kept in cages. 

 Dr. Reeve says he has known several attempts 

 made to keep swallows in a warm room during 

 winter without success ; but M. Natterer kept a 

 number of swallows in cages for eight or nine 



* Travels in the Two Sicilies, iv., 115. 



