high-power microscope a little spherical liquid-holding cavity, which slowly enlarges, then bursts at the surface and collapses. After a brief interval it forms again, and again bursts to the exterior. In the "bell-animalcule " -a beautiful active little creature only one-thousandth of an inch in diameter—it may be seen to form, swell, collapse, and re-form as often as twenty times in a minute (see Fig. 41). Soluble colouring matter taken in by the animalcule with food is excreted by the liquid accumulated in and ejected to the exterior by this spherical chamber. It is called the "pulsating" or "contractile" vacuole, and by its rhythmical pulsating movement of dilatation and collapse presents definite points of similarity to the alternately dilating and contracting hearts of higher animals. The entering flow of liquid here, as in the veins and heart of higher animals, is continuous. The rhythm is due, as is the rhythm of the heart, to the alternation of a brief period of activity or contraction, and a brief period of consequent exhaustion, rest, and repair on the part of living contractile substance.

XVII

SLEEP

A

N enterprising journalist has recently published the replies of a number of well-known men to an inquiry as to how many hours' sleep they are in the habit of taking, and what they find to be the best remedy for sleeplessness. Such an inquiry naturally leads on to further thoughts about "Sleep." What a mysterious, yet sweet and lovable thing it is! How strange it is that we all regularly and gladly abandon ourselves to it! cannot do so!

How terrible is the state of those who And then one is led to ask, what is it? Do all living things sleep for some part of the twenty-four hours? How does it differ from mere resting, and in what does its virtue consist?

and why is it?

Shakespeare has said the most beautiful words that have ever been uttered about sleep, and that because he knew what it was to seek for it in vain—

“Methought I heard a voice cry, 'Sleep no more!
Macbeth does murder sleep,' the innocent sleep;
Sleep, that knits up the ravell'd sleave of care,
The death of each day's life, sore labour's bath,
Balm of hurt minds, great Nature's second course,
Chief nourisher in life's feast."

And again, when the strenuous life of the great Bolingbroke has at last overtaxed his brain, and he can

no more find rest and unconsciousness at night, Shakespeare makes him say

"How many

thousand of my poorest subjects

Are at this hour asleep! O sleep, O gentle sleep,
Nature's soft nurse, how have I frighted thee,
That thou no more wilt weigh my eyelids down,

And steep my senses in forgetfulness?

Why rather, sleep, liest thou in smoky cribs,

Upon uneasy pallets stretching thee,

And hush'd with buzzing night-flies to thy slumber,
Than in the perfum'd chambers of the great,

Under the canopies of costly state,

And lull'd with sound of sweetest melody?”

Poets have as a rule been too ready to make much of the likeness of sleep and death, whereas there is an absolute difference in their mere appearance. Sleep makes even those who are ill-favoured and coarse look beautiful, imparts to its subjects a graciousness of expression and of colour, and a gentle rhythmic movement, whilst suffusing them as it were with an “aura” of contented trustfulness. These things are far from the cold stillness of pallid death. And this depends upon the fact that in sleep, though many of the activities of the body and mind are checked, and even arrested, there are yet still present the never-ceasing pulse of the heart, the flow of the blood, the intake and output of the breath, and a certain subdued but still active tension of muscles, so that though the body and limbs are relaxed they never assume the aspect of complete mechanical collapse which we see in death. The pupils of the eyes are strongly contracted during sleep, not relaxed and expanded as are those of wide-awake people in the dark. There are some well-known works of art both painting and sculpture-in which the dead are not truly represented, but are made to retain the

resistfulness and pose of living men and women; others show true observation in presenting the startling and distinctive flaccidity of the newly dead, which is followed after a few hours by the equally characteristic rigor mortis, or stiffness of the dead. There are many fine studies of sleep by sculptors, but none which to my thinking so delicately and truthfully present its most beautiful and peculiar effects on the muscular "tone" as a work in the Luxembourg Gallery in Paris, called "Le Nid "—a baby of a year old and a little girl of three or four years, asleep side by side on the cushion of a capacious arm-chair. The pose and the details of muscular relaxation differ greatly and characteristically in the two children. One would like to see sleep at different ages and under various conditions of fatigue similarly portrayed, for there is a range and variety of expression in those who sleep, not perhaps as extensive, but as beautiful as that to be found in those who are awake.

All things on the earth may be said (if we use the term in a wide sense) to sleep, for all are affected by the stimulation to activity caused by sunlight and by its cessation during night. It is only of late years that we have come to know of fishes, crabs, worms, and starfishes (many of them without eyes) which live in the depths of the ocean, where no light penetrates and it is always night. The ultimate source of their food is in the upper sunlit layers of water, to which they never penetrate, and from which particles of dead but nutritious matter (the bodies of those who have lived up there) rain down upon them incessantly, like manna on the Israelites. All things accessible to the sun's rays are not equally, nor even similarly, affected by the alternation of day and night, and some not directly at all, but only by the sleeping and waking of

other things. The food of all living things comes ultimately from plants which, in the presence of sunlight, and only in that presence, and in virtue of its action upon their green leaves, manufacture starch and sugar from the carbonic acid which exists in the air and water around them, whilst they are also thus enabled to take up nitrogen, and so to form their living substance or protoplasm. At night those particles or cells of the living protoplasm of plants which are furnished with transparent green granules, so as to entangle the sunlight, and by its aid feed on carbonic acid, cease this work. They necessarily repose from their labour because the light has gone. This is the simplest example of the sleep of living things. And that here, too, as in higher creatures, sleep is not a merely negative thing—a mere cessation is shown by the fact that it is at night that other changes go on in the plant. The manufactured food takes effect on the cells or particles nourished by it; in the night the well-fed, enlarged "cells" in the growing parts of many plants slowly divide each one into two, and each of these again into two, and so on, so as to increase their total number and produce growth and development of the plant. This alternation of activities in day and night occurs even in the invisible microscopic vegetation of pools and streams. Animals-even the most minute, only visible with a strong microscope— move about in search of "bits" of food-in fact, bits of other animals or of plants-and they, too, are, with special exceptions, checked in their search for food by the darkness, for even extremely minute and simple animals are guided in their search by light—that is to say, by a more or less efficient sense of sight. Thus we see that in a general way the sun is truly the ruler of life, and that when he is hidden from us we all become quiescent, a condition which may be rightly considered