3. The heart draws this fluid from the lung along with the air. But while it must necessarily expel the air once this has performed its service, by the route by which it drew it in, it allows some of the fluid to dribble into its sheath, letting the rest pass out along with the air. In this way too the breath, when it runs back, raises the palate. Of course the breath must run back in due course, since it is not food - how could mere air and water be food for man? They are rather a compensation for an innate deficiency.