[78a]
Thereupon they arranged the irrigation on some such plan as this—a plan which we shall perceive more easily when we have first agreed upon the following postulates. All bodies composed of smaller particles shut in the larger, but those composed of larger particles cannot shut in the smaller; and fire, because of all the elements it has the smallest particles,1 passes through water and earth and air and all things composed thereof, and nothing can shut it in. We must conceive that the same law holds good of the action of our belly. Whenever foods and drinks flow into it