we find blood in motion, the process of appropriation is going on. The circulation is the surest sign of life. Muscles retain irritability for an hour or two after circulation ceases, but irritability is not life. Death is owing to the absence of this process of appropriation.

Bichat has divided life into two varieties, the organic and the animal. The first is common to both vegetables and animals, the last is peculiar to animals alone. Organic life applies to the functions which nourish and sustain the object-animal life to those which make it a sentient being; which give it thought, feeling, and motion, and bring it into communication with the surrounding world. The processes of assimilation and excretion exist both in animals and vegetables: the other vital processes are restricted solely to animals. The digestive organs, the kidneys, the heart, and the lungs, are the apparatus which carry into effect the organic life of animals. Those which manifest animal life are the brain, the organs of the senses, and the voluntary powers. Sleep is the suspension of animal life; and during its continuance the creature is under the influence of organic life alone.

Notwithstanding the renovating influence of sleep, which apparently brings up the lost vigour of the

frame to a particular standard, there is a power in animal life which leads it almost imperceptibly on from infancy to second childhood, or that of old age. This power sleep, however healthy, is incapable of counteracting. The skin wrinkles, and every-where shows marks of the ploughshare of Saturn; the adipose structure dissolves; the bones become brittle; the teeth decay or drop out; the eye loses its exquisite sensibility to sight; the ear to sound; and the hair is bleached to whiteness. These are accompanied with a general decay of the intellectual faculties; there is a loss of memory, and less sensibility to emotion; the iris hues of fancy subside to twilight; and the sphere of thought and action is narrowed. The principle of decay is implanted in our nature, and cannot be counteracted. Few people, however, die of mere decay, for death is generally accelerated by disease. From sleep we awake to exertion-from death not at all, at least on this side of time. Methuselah in ancient, and Thomas Parr in modern times ate well, digested well, and slept well; but at length they each died. Death is omnivorous. The worm which crawls on the highway and the monarch on his couch of state, are alike subjected to the same stern and inexorable law; they alike become the victims of the universal tyrant.

CHAPTER II.

SLEEP IN GENERAL.

EVERY animal passes some portion of its time in sleep. This is a rule to which there is no exception; although the kind of slumber and the degree of profoundness in which it exists in the different classes are extremely various. Some physiologists lay it down as a general rule, that the larger the brain of an animal the greater is the necessity for a considerable proportion of sleep. This, however, I suspect is not borne out by facts. Man, for instance, and some birds, such as the sparrow, have the largest brains in proportion to their size, and yet it is probable that they do not sleep so much as some other animals with much smaller brains. The serpent tribe, unless when

stimulated by hunger, (in which case they will remain awake for days at a time waiting for their prey,) sleep much more than men or birds, and yet their brains are, proportionally, greatly inferior in size the boa, after dining on a stag or goat, will continue in profound sleep for several days. Fishes, * indeed, whose brains are small, require little sleep; but the same remark applies to birds,† which have large brains, and whose slumber is neither profound nor of long continuance. The assertion, therefore, that the quantum of sleep has any reference to the size of the brain may be safely looked upon as unfounded. That it has reference to the quality of the brain is more likely, for we find that carnivorous

As a proof that fishes sleep, Aristotle, who seems to have paid more attention to their habits than any modern author, states, that while in this condition they remain motionless, with the exception of a gentle movement of the tail-that they may then be readily taken by the hand, and that, if suddenly touched, they instantly start. The tunny, he adds, are surprised and surrounded by nets while asleep, which is known by their showing the white of their eyes.

The sleep of some birds is amazingly light. Such is the case with the goose, which is disturbed by the slightest noise, and more useful than any watch-dog for giving warning of danger. It was the cackling of the sacred geese that saved the capitol of Rome from the soldiers of Brennus, when the watch-dogs failed to discover the approach of the enemy.✓

animals sleep more than such as are herbivorous; and it is probable that the texture, as well as form, of the brains of these two classes is materially different. This remark, with regard to the causes of the various proportions of sleep required by the carnivorous and herbivorous tribes, I throw out not as a matter of certainty, but merely as a surmise which seems to have considerable foundation in

truth.

In proportion as man exceeds all other animals in the excellency of his physical organization, and in intellectual capability, we shall find that in him the various phenomena of sleep are exhibited in greater regularity and perfection. Sleep seems more indispensably requisite to man than to any other creature, if there can be supposed to exist any difference where its indispensability is universal, and where every animal must, in some degree or other, partake of it; but, as regards man, it is certain that he sustains any violation of the law ordaining regular periods of repose with less indifference than the lower grades of creation-that a certain proportion of sleep is more essential to his existence than theirs -that he has less power of enduring protracted wakefulness, or continuing in protracted sleepand that he is more refreshed by repose and more