It may be said that GALEN expresses, in these passages, the Platonic dogma of an _anima mundi_. But they certainly agree with the sentiments of HIPPOCRATES; and whether he derived them from the former or the latter, matters not, as both of them have invested matter with certain qualities, which render it active, whether it be so essentially or by the act of the Creator. GALEN may be also regarded as partially an Epicurean; for he insists that there are several sorts of matter, or as we should say, several elements; but he differs from that sect again in affirming for it a passible quality. To show that there must be more than one element, or kind of matter, he says, that if there was only one element, or a unit, it would be impassible; it could undergo no change whatever. For there would be nothing by which it could be made to suffer any alteration, or into which it could be altered. Whatever is changed, is changed into something else, and whatever suffers, suffers from something extrinsic: therefore he affirms, that of necessity there must be several sorts of matter, or elements. He says, "there are only two theories on this subject deserving our attention; one of which affirms that sentient bodies are composed of elements possessing the faculty, (cum patiendi tum sentiendi,) both of suffering and perceiving an alteration;" while the other affirms that such bodies are formed (ex patibilibus, sed sensu expertibus) out of passible, but not sentient elements. Neither of these doctrines does he consider tenable, so long as only one element is affirmed, as earth, air, or fire alone, which could never become capable of that great variety of actions we witness in living bodies: but, admit several elements, and we suppose that the mutual interchange of powers would yield a compound body, capable of all the vital phenomena. Such, therefore, says he, as consider the human body to be composed of fire, air, earth, and water, mutually transmuted, alternated, and reduced to a given temperament, and thereby vested with a sentient faculty, speak reasonably; and it is evident that there must be more than one element, and that these elements are passible bodies. PLATO had taught, that, though all bodies are formed of matter, yet matter itself is not a body; and the same idea is conveyed by ARISTOTLE, in the Lib. de partibus animal. & earum causis, II c.i. "Prima statui potest ea quae ex primordiis conficitur, iis quae nonnulli elementa appellant terram dico, aquam aerem & ignem: sed melius fortasse dici potest ex virtutibus confici elementorum, iisque non omnibus sed ut ante expositum est humiditus enim, & siccitas, & caliditas, and frigiditas, materia sunt corporum compositorum."