— On The Nature of Things, Lucretius

This mental nature, therefore, or compound intellectual substance, is contained in every body, and is itself the guardian of the body, and the cause of its safety; for the two, the body and the soul, cohere, as it were, by common roots, with one another, nor seem capable of being torn asunder without destruction of both. For as it is impossible to separate the perfume from balls of frankincense, without the nature of it, at the same time, being destroyed, so it is impossible to extract the nature or substance of the mind and soul from the whole body, without all parts being dissolved…