Plutarch Conjugalia Praecepta 34

[34] Philosophers assert that, of bodies which consist of several parts, some are composed of parts distinct and separate, as a navy or army royal; others of contiguous parts, as a house or a ship; and others of parts united at the first conception, equally partaking of life and motion and growing together, as are the bodies of all living creatures. Thus, where people wed for pure affection, that marriage may be said to resemble those bodies whose parts are solidly fixed together. They who marry for the sake of great portions, or else desirous of offspring, are like to bodies whose parts are contiguous and cleave close to one another; and they who only bed together, if there be any such, resemble bodies whose parts are distinct and without dependency. Now, as physicians say that liquids are the only bodies which most easily intermix without any difference of propriety or respect one with another; so should it be said of people joined together in matrimony, that there is a perfect mixture of bodies and estates, of friends and relations. Therefore the Roman law prohibits new married people from giving and receiving mutual presents one from another; not that they should not participate one with another, but to show that they were not to enjoy any thing but what they possess in common.