We share with other animals the great blessing of Sleep, nature's soft nurse, "the mantle that covers thought, the food that appeases hunger, the drink that quenches thirst, the fire that warms cold, the cold that moderates heat, the coin that purchases all things, the balance and weight that equals the shepherd with the king, and the simple with the wise." Some animals dream as we do; Dogs, for instance, evidently dream of the chase. With the lower animals which cannot shut their eyes it is, however, more difficult to make sure whether they are awake or asleep. I have often noticed insects at night, even when it was warm and light, behave just as if they were asleep, and take no notice of objects which would certainly have startled them in the day. The same thing has also been observed in the case of fish. But why should we sleep? What a remarkable thing it is that one-third of our life should be passed in unconsciousness. "Half of our days," says Sir T. Browne, "we pass in the shadow of the earth, and the brother of death extracteth a third part of our lives." The obvious suggestion is that we require rest. But this does not fully meet the case. In sleep the mind is still awake, and lives a life of its own: our thoughts wander, uncontrolled, by the will. The mind, therefore, is not necessarily itself at rest; and yet we all know how it is refreshed by sleep. But though animals sleep, many of them are nocturnal in their habits. Humboldt gives a vivid description of night in a Brazilian forest. "Everything passed tranquilly till eleven at night, and then a noise so terrible arose in the neighbouring forest that it was almost impossible to close our eyes. Amid the cries of so many wild beasts howling at once the Indians discriminated such only as were (at intervals) heard separately. These were the little soft cries of the sapajous, the moans of the alouate apes, the howlings of the jaguar and couguar, the peccary and the sloth, and the cries of (many) birds. When the jaguars approached the skirt of the forest our dog, which till then had never ceased barking, began to howl and seek for shelter beneath our hammocks. Sometimes, after a long silence, the cry of the tiger came from the tops of the trees; and then it was followed by the sharp and long whistling of the monkeys, which appeared to flee from the danger which threatened them. We heard the same noises repeated during the course of whole months whenever the forest approached the bed of the river.