From this account, then, it appears that when we sleep we not only lose the sensibility to external objects, and the power of volition, but also that ideas acquire such an increase of relative or absolute liveliness as to give all the feeling of reality or outward existence, and, in feet, introduce us for the time into a new world.

I shall now, in order to vary this discourse, remark the different tendencies to sleep in different animals, and in different individuals of the human species.

It is probable that all animals pass at some time or other into the state of sleep, since periodicity of action seems a universal property of the Amotions which characterize an animal. Little is known of the phenomena of sleep in animals which range below the vertebrated classes, and have less complicated nervous systems. Periods of inactivity are with them, perhaps, periods of sleep. Fishes are known to sleep, and Aristotle tells us how they may be surprized in their slumbers. Reptiles often sleep for very long periods, especially serpents, when they have been provided with food enough to last them for several weeks' digestion. Birds take much shorter periods of repose, and the mammalia likewise, excepting those which pass periodically into the state of hybernation, which is a profound degree of sleep. Setting aside, for the present, this state, we may observe that the capability of sleeping for a long period bears a relation to the digestive function of the animal. If it needs frequent supplies of food, those organs which provide it must be correspondingly active. But if a large quantity can be laid up in store, the senses and muscular movements may be suspended during its slow digestion; and this, as we have said, is the case with serpents. Many beasts of prey, which continue watchful for several days, when hungry, will remain torpid for a long time after they have gorged themselves with food. Man, who has a greater power than any other animal of accomodating himself to varying circumstances, has often acquired the habit of long fasts, making large meals, and spending a corresponding time in sleep. It is one of the accomplishments of the aboriginal civilization of North America to be able to lay in a stock of food for two or three days, and to sleep in long spells, in order to be able to bear long abstinence and watching. There are many curious cases on record of persons capable of long slumbers. "Quin, the celebrated player," says Dr. Macnish, "could slumber for 24 hours successively. Elizabeth Orvan spent three fourths of her life in sleep. Elizabeth Perkins slept for a week or fortnight at a time. Mary Lyall did the same for six successive weeks. In Bowyer's Life of Beattie a curious anecdote is related of Dr. Reid, viz., that he could take as much food, and immediately afterwards as much sleep, as were sufficient for two days."

I cannot leave this part of my subject without noticing the fact that animals give evidence of dreaming. It was not a mere poetical speculation which led that accurate observer of the habits of animals, Sir Waiter Scott, to say,

"The Stag hounds, weary with the chase,

Lay stretched upon the rushy floor ; And urged, in dreams, the forest race,

From Teviot Stone to Eskdale Moor."

Lucretius describes the indications of dreaming in the lower animals with great minuteness. He even points out the difference observable in the dreams of dogs of chase from those of the lap-dog.

" Venantumque canes in molli sæpe quiete Jactant crura tamen subito, yocesque repente Mittunt, et crebras reddncnnt naribiis auras, Ut vestigia si teneant inventa ferarnm. Expergefactique sequuntur inania sæpe Cervorum simulacra, fugæ quasi dedita cernant; Donec disenssis redeant erroribus ad æ. At consneta domi catulornm blanda propago Degere, sæpe levem ex oculis, volucremque soporem Discutere, et corpus de terra conripere instant, Proinde quasi ignotas facies, atque ora tuantur."*

We must all of us have noticed that dogs growl and snap in their sleep, as if angry, and sometimes whine, or wag their tails, as if more amiable emotions were playing oyer their slumbers. Horses are said to neigh and rear in their sleep ; and parrots, the most intelligent of the winged race, are reported by those who have studied them to give unequivocal signs of dreaming.

The sleep of animals cannot be dismissed without one or two comments on that remarkable condition called Hybernation. A few animals only, as the hedgehog, the dormouse, the marmot, the hamster, and the bat, are known to pass into this state at certain periods. A great deal of mystery once hung over this subject, and the animal was thought whilst hybernating to have its whole life suspended but not extinguished. The state is now known to be one of profound sleep. And not only are the animal functions brought into a state of complete inactivity, but even those of the organic life are reduced to the lowest ebb compatible with the continuance of vital action. The respiration can scarcely be detected, and the circulation is wonderfully slackened. Thus, " in the hamster the pulse usually beats at the rate of 150 per minute, but it is reduced to 15 in the torpid condition. Marmots, in a state of health and activity, perform about 500 respirations in an hour; but in the torpid state these occur only about 14 times during the same period, and are executed with intervals of four or five minutes of absolute rest, and without any considerable enlargement of the chest." * The bat feeds upon insects, but in winter the insects disappear; therefore the Creator has beneficently arranged that during that season the bat shall pass its time in a deep lethargy, not requiring food, because little or no nourishment is then expended. The hedgehog wakes up after two, three, or four days, and obtains a few snails or worms, if the ground is not too hard. The dor-mouse may wake every day, for a short time, when it eats a few grains if it can find them, and relapses into sleep. The temperature of these animals falls very nearly to that of the atmosphere, which is a further illustration of how little is the amount of vital action of which they are the subjects. But it is not because they are cold that they become lethargic. The state of hybernation is quite distinct from the torpor occasioned by loss of heat.