( xiii ) 
pid or other state, during the winter-season, seems rather to strengthen, than to weaken, the argument, that these 
birds are, 'n general, migratory birds. If all these birds continued among us, many of them would be found. 
The labours of one century, or more, in cutting down the timber of the forest, in blowing rocks, in draining mill- 
ponds, and marshes, would furnish more than five or six instances (and they not always quite so well authenti- 
cated as we could wish) of Swallows, &c. being found during the winter-season, in a benumbed state. 
§. XXVII. 
The argument derived from the torpid state into which so many of our animals are observed to fall upon the ap- 
proach of winter, is of less weight than may, at first sight, be imagined. These animals are much less capable of 
migrating than the birds. If they were capable of making long journies to more favourable climates, I do not doubt 
they would make them. For I am persuaded, by a variety of experiments and observations which I have made, and 
may, perhaps, be induced to communicate to the public at some future period, that most of our hybernating ani- 
mals go with reluctance into this state. I am even of opinion, that the state of torpidity of many animals is a state 
of pain and sufferance. This observation, at least, seems to hold good with respect to those animals (and I believe 
they constitute the greater number of the hybernating animals) which divide the winter between sleeping and wak- 
ing : which, in other words, under the influence of cold and other causes, fall into a kind of profound sleep, during 
which the functions of the heart and the lungs are constantly performed ; and even that of the stomach and intes- 
tines, in some measure, goes on : and during all which time, such animals are sensible to the influence of mecha- 
nical and other stimuli. This class of hybernating quadrupeds often, during the course of the winter, spontaneously 
awake from their slumber, take food, and fall into slumber, again. I do not, however, imagine, that animals, which 
are so torpid as to be incapable of being roused by the application of the most powerful stimuli, can be said to be in a 
state of pain and sufferance. But I believe, that the number of these continual sleepers is very small, even in the 
coldest climates. 
§. XXVIII. 
I 
We are certain, that the torpid state of many animals is altogether an accidental circimistance : that is, it is not 
necessary to the species. I will not assert, with my learned and ingenious friend, Mr. Fabricius, that it is not natural 
to, nor coeval with, the species. It would be difficult to prove this position : but the position which I have advanced 
may be maintained. Animals of the same species have often a very extensive range over the world. Thus, the Ursus 
Lotor, or Raccoon, extends from Lake-Superior to the West-India-Islands, and the warm parts of South-America. 
The Opossum has a range not much less extensive. I trace the Rattle-Snake (Crotalus horridus) as far north as the 
Bay of Saguena, on Lake-Huron, and it is known in the country of Brasil. In such extensive tracts of country, these 
inimals are exposed to very different degrees of temperature : on the one hand, to a great alternation of heat and 
^old; on the other hand, to a perpetual spring and summer. We ought not, therefore, to expect to find any of 
:hem torpid in the whole of this extensive range. In fact, several of those animals which become torpid in the 
lorthern parts of our country do not fall into this state in the southern and warmer climates.* As cold, however, 
3 not the only cause of the torpidity of animals, we must not be surprized to find instances of animals becom- 
ng torpid in climates that are warm. Extreme heat, like extreme cold, seems to predispose the animal system to 
his state, particularly, perhaps, when there is a deficiency of food. 
§. XXIX. 
We see that quadrupeds and some other animals do occasionally, during severe winters, migi'ate to more southern 
•limates. I am assured, that the Bears migrate, in great numbers, every autumn, across the Mississippi, going south 
perhaps to the mountains of New-Mexico), in search of a milder climate. In the spring, they return again by 
See my account of the Dipue Americanus, or American .Jerboa, in the 4th volume of the Transactions of the American Philosophical Society. 
