HEAT AND LIFE. 151 
The influence of cold on organized beings varies, ac- 
cording as we regard superior animals or the inferior spe- 
cies. In general, it may be said that it requires a very low 
surrounding temperature to chill many animals, because the 
vital heat they develop resists the process with energy. 
Yet the mammals of arctic regions, in spite of their thick 
coat of fur, can only brave the temperature of the pole 
—sometimes equal to 40° (cent.) below zero, the freezing- 
point of mercury—by living under the snow where they 
make their lair. The Esquimaux, too, dig huts in it, where 
they pass their wretched days. When the organism can 
neither react nor protect itself against temperatures so low, 
death by freezing quickly overtakes it. The body is stiff- 
ened, and retains afterward a state of remarkable incorrupti- 
bility. Every one knows the story of the antediluvian mam- 
moths discovered in the polar ice, where they had been bur- 
ied, as fresh as animals just dead. While heat destroys the 
tissues, cold preserves them. 
Through what mechanical means does cold become mor- 
tal? It seems to act on the nervous system. Travelers 
relate that in polar regions an unconquerable disposition to 
sleep overcomes men attacked by very low temperatures. 
On the icy shores of Terra del Fuego, Solander said to his 
companions, ‘‘ Whoever sits down. falls asleep, and who- 
ever falls asleep never wakes again.” This inclination is 
so overpowering that many of his attendants gave up to it, 
and he himself sank down for a moment on the snow. it is 
said that, during the winter of 1700, two thousand soldiers 
of Charles XII.’s army perished in the sleep to which they 
surrendered, under the influence of cold. Its action on the 
nervous centres, however, is only secondary and consequent 
on another phenomenon, studied by Pouchet, which reveals 
this as the secret of death. When the temperature of the 
interior of the body sinks to 10° or 12° below zero (cent.), 
the cold freezes the blood more or less, thoroughly disor- 
