The primary matter they make the substratum of all things : so Chrysippus in the first book of his Physics, and Zeno. By matter is meant that out of which anything whatsoever is produced. Both substance and matter are terms used in a twofold sense according as they signify (1) universal or (2) particular substance or matter. The former neither increases nor diminishes, while the matter of particular things both increases and diminishes. Body according to them is substance which is finite : so Antipater in his second book On Substance, and Apollodorus in his Physics. Matter can also be acted upon, as the same author says, for if it were immutable, the things which are produced would never have been produced out of it. Hence the further doctrine that matter is divisible ad infinitum. Chrysippus says that the division is not ad infinitum, but itself infinite ; for there is nothing infinitely small to which the division can extend. But nevertheless the division goes on without ceasing. Hence, again, their explanation of the mixture of two substances is, according to Chrysippus in the third book of his Physics, that they permeate each other through and through, and that the particles of the one do not merely surround those of the other or lie beside them. Thus, if a little drop of wine be thrown into the sea, it will be equally diffused over the whole sea for a while and then will be blended with it. Also they hold that there are daemons (Sat/xoi'e^) who are in sympathy with mankind and watch over human affairs. They believe too in heroes, that is, the souls of the righteous that have survived their bodies.