The Cause of Suction

Abstract

Since the air enveloping the earth presses upon it so heavily, it follows that air penetrates and fills all cracks and interstices of bodies (unless the bodies are perfectly solid.) Now if this is the case, then air also fills the bodies and all the cavities of animals and in so doing it renders them unaware of its pressure. Once a body is filled, however, it takes in nothing more, but rejects it. However, a container outside a body which is not filled, but is empty, or at least partially empty, is attached or connected to it and this body is subjected to pressure (just as our bodies and all things existing in these lower regions are pressed by the weight of air), of necessity whatever is fluid in it passes into the attached empty container so as to fill it. For example, the human body is pressed on all sides by surrounding air, but once it has been completely filled,’the pressure of the encompassing air is imperceptible. When, however, an infant is placed upon such a body at the breast of its mother, for instance, and creates an empty space in its mouth by retracting its tongue, that is, when it sucks the fluid, or milk, which is near the surface, air is necessarily directed into the infant’s empty mouth through the pressure on the body and breast.