76 On Hybernation. 
J : 
pose is not absolutely necessary, as some authors on this sub- 
ject have supposed. {tis not therefore requisite to the ani- 
mal economy, as in sleep, to prepare it for further exertions. 
he number of animals that igen is — greater 
than we generally imagine. Dr. Reeve says “the num- 
ber of hy bernating animals is phate eh iss of those 
which remain sig ee by cold” p. 5. When the ther- 
mometer sinks to about 50°, animals that hybernate retire 
to their biding tag in trees, rocks, and the earth, where 
will be most secure from their enemies. Here they 
roll themselves up, exposing the least possible surface to 
tke action of the air, and remain in a quiescent state until 
the return of a more vertical sun warms them into life. Dr. 
Reeve’s ideas on the ‘ani i of cold on the system are so 
good I quote them at Jeng 
“The cessation of elke action seems owing to 
the lowered sae beain re of the muscles themselves, 
because, when e transmission of nervous Doli is 
of the muscular meal? er that _ is caused a the ac- 
tion of cold, and by suspended respiration; the capillaries 
of the vascular system appear to become contracted by the 
loss of animal heat ; and this diminution always begins at 
the surface of the body and gradually increases to the cen- 
tre, as observed in examples of numbness from cold, and in 
applying the thermometer to different parts_ oe anithals 
whilst they are gradually becoming torpid. see th 
animals resist the propensity to torpor, until by the gradual 
pa of their heat and the want of a supply from the 
rption of oxygen at their lungs, and at the surface 
dacie bodies, the irritability is so far lessened that it becomes 
itself a cause of its own deficiency, by arresting the respi- 
ration, and consequently depriving the heart of its supply, 
which is furnished by the coronary arteries.’ — Reeve, 
p- 55, 
Spatisbneni never found the temperature of torpid ani- 
mals below 36° although exposed to a much greater degree 
of cold. In this situation, the action of the digestive and 
