In the whole of its growth the soul needs continually to be refreshed by the inbreathing of air, and to be sustained by exhalations from the blood[122]. Here we touch upon one of those fundamental doctrines of the system, derived by Zeno from Heraclitus[123], which bind together the great and the little world. Just as the heavenly bodies are maintained by exhalations from the Ocean[124], so the soul is dependent upon the body for its daily food. Hence follows the important consequence that weakness and disease of the body react upon the soul; the philosopher must keep his body in health for the soul’s good, if for no other reason[125]. If the Stoics in discussing problems of ethics constantly maintain that the health of the soul is independent of that of the body, such statements are paradoxical and need qualification[126]. [Sidenote: Sleep and death.] =290.= The mutual action of body and soul is most readily illustrated by sleep. The Stoics do not hold, as the Animists do, that the soul quits the body in sleep; nor do they agree with another popular view, that the soul then quits the extremities of the body and concentrates itself at the heart[127]. Sleep is due to a relaxation, contraction, or weakening of the spirit[128]; a lowering of its grade, which nevertheless is clearly no sign of ill health. In old age there is often an imperfection of the reason, and this is also seen in the sick, the tired, and the anaemic[129]. In death there is a complete relaxation of tone in the breath that we can feel, that is, in such spirit as belongs to the body[130]; there follows the separation of soul from body. [Sidenote: The beyond.]