204

Phenomena of Hibernation.

The power of producing heat seems to be different at different seasons. Dr. Edwards artificially exposed five sparrows to the influence of a low degree of temperature during three hours at different periods of the year. In February the heat lost averaged at 0°.4 Cent, in July at 3°.62 Cent, in August at 4°.87 Cent. The constitution thus adapts itself to the temperature in which it is placed: when less heat is called for, less heat is habitually produced; and the power of producing it in large quantity is temporarily lost.

Animals that hibernate remain during life unable to sustain a standard temperature against any considerable external cold. In the month of April, the air being at 16° Cent, Dr. Edwards exposed a bat to the temperature of 1° for an hour: in this time its temperature fell from 34° to 14°. Adult sparrows and Guinea pigs under corresponding circumstances lost from 2° to 3° only.

Animals of this description on the approach of winter seek to envelope themselves in substances which contribute to prevent the abstraction of heat and the access of fresh air, and then fall into a torpid state, during which they take no nutriment; and their breathing and the circulation of the blood are so languid, that the performance of these functions has been doubted.

During the torpid state the temperature of the body falls nearly to that of the surrounding media: if the animal be roused, its temperature becomes elevated.

The air of the apartment being 1°.5 Cent, the temperature of a torpid bat was 4°. M. de Saissy roused it by mechanically disturbing it. The animal took an hour to wake: at the expiration of thirty minutes its temperature had risen to 15°, when fully roused, to 27°. The

Effects of extreme Cold.

205

temperature of a dormouse under similar circumstances rose to 36°, its standard heat.

It is remarkable that cold serves as a means of waking hibernating animals, as well as mechanical excitement or a high temperature. M. de Saissy carefully exposed a torpid dormouse at a window looking to the north, when the centigrade thermometer stood at -4°. After a period somewhat longer than in the preceding experiment, the animal was roused, and its temperature rose to 36°. But in this instance the cold which wakes the animal from its torpid state becomes quickly fatal; the temperature falls again, and the animal sinks into a lethargy which is mortal.

The hibernating animal thus perishes of cold like other animals.

In human beings, when sufficient heat cannot be produced to meet the demand from without, the temperature of the body falls, excessive drowsiness and inclination to sleep is felt, which, when indulged in, proves fatal. The frame is then in a condition the least calculated to resist the effects of cold; as heat is habitually produced in greater quantity during the waking state than in sleep, during exercise than during repose. Dr. Edwards made the curious remark that the power of enduring and recovering from the effects of cold in young animals, is inversely as their power of producing heat; so that kittens or puppies newly-born can live for two or three days at a temperature of 20° Cent, or even two or three degrees below it.

The accumulation of heat in the system is no less fatal

• De l'Influence &c. p. 474.

206

Effects of great Heat on the System.

than its rapid abstraction. Copious perspiration and intense thirst, difficulty of breathing, violent pain in the breast, and palpitation of the heart, followed by insensibility, were the symptoms remembered by one who survived the imprisonment in the black hole at Calcutta. Of 146 who shared these sufferings, twenty-three only survived one night's confinement in a crowded dungeon during a tropical night". These fatal effects appear to have ensued in consequence of the hot and confined air becoming saturated with moisture, which prevented further evaporation from the skin, and kept the heat of the body permanently raised above the usual standard. M. Delaroche has ascertained by experiment, that animals placed in an atmosphere charged with moisture cannot support a degree of heat slightly raised above their natural standard.

Sir C. Blagden observed, when exposed for a few minutes with his clothes on and after a hearty repast to a temperature of 240°, an oppression upon the chest, attended with a sense of anxiety; and the pulse was found to beat 144 pulsations immediately upon leaving the heated room. Upon exposing himself in the forenoon after a moderate breakfast to the temperature of 220° without his shirt, the impression of the heated air was at first painfully disagreeable; but in five or six minutes a profuse sweat broke out, which gave instant relief, and took off all the extraordinary uneasiness: at the end of twelve minutes he left the room very much fatigued, but no otherwise disordered; his pulse had risen to 136.i

h Dodsley's Annual Register, 1758. i Phil. Trans. vol. lxv. p. 489.

CHAPTER XI.

OF THE BRAIN AND NERVES.

SECTION 1.

Of the Elements of a Nervous System, and of Con

sciousness.

THE polype, which was divided in the experiments of Trembley, is a thin gelatinous tube about an inch in length, closed at its narrower end. From the margin of its open extremity a fringe of long and slender filaments or tentacula is produced. Every part of the polype is contractile: by means of its tentacula it discriminates and seizes its prey, and conveys it into its digestive cavity; it moves from place to place by alternately attaching either extremity: its structure seems a jelly containing innumerable granules. When turned insideout the new internal surface acquires the faculty of digestion: when divided, each half becomes a complete polype.

Thus in the lowest animals the properties of life seem equally diffused throughout their substance: each half of a polype may form a portion of a sentient being, or become upon mechanical division individualized.

Cuvier has arranged the diversified species of animals under four classes, which consist, 1. of radiated, and 2. of articulated animals; 3. of mollusca, and 4. of vertebral animals. The polype is nearly at the commence

207

206

Effects of great Heat on the System.

than its rapid abstraction. Copious perspirat
intense thirst, difficulty of breathing, violent y
breast, and palpitation of the heart, follower
bility, were the symptoms remembered by
vived the imprisonment in the black

Of 146 who shared these sufferings

survived one night's confinement in
during a tropical night. These
have ensued in consequence of
becoming saturated with moist
ther evaporation from the sk
body permanently raised a
Delaroche has ascertain
placed in an atmosphe
support a degree of
tural standard.

Sir C. Blagden
nutes with his cl
temperature of

tended with

to beat 14/

heated ro

after a ▾
withou
at fir

ar

System, and of Con

experiments of

out an inch in

argin of

CHAPTER XI.

BRAIN AND NERVES.

- U two

wo chords, one

of the body, upon which

erally placed; and secondly, of

erves, derived from the central organ

it surfaces or contractile parts of the animal. star-fish (a radiated animal) the central organ

a psts of a ring of white nervous matter, which surrounds the orifice of the stomach, and gives off opposite the centre of each ray nerves for its supply.

to

In the centipede (an articulated animal) the central organ consists of a double chord extending its whole length immediately within the integuments of the abdomen at the middle of each intersection a nodule is

!