Yogācārabhūmi Śāstra, Fascicle 34 (29)

Original text:云何观察库藏变异无常之性。谓由观见种种库藏。一时盈满一时灭尽。见此事已。便作是念。如是诸行。其性无常。余如前说。云何观察饮食变异无常之性。谓由观见种种饮食。一时未办一时已办。一时入口牙齿咀嚼。和杂涎唾细细吞咽。一时入腹渐渐消化。一时变为屎尿流出。见此事已。便作是念。如是诸行。其性无常。余如前说。

Explanation: How does one observe the impermanent nature of the transformation of storehouse matters (koṣṭhāgāra-vastu)? One observes that various storehouses are at one time full and abundant, and at another time depleted and exhausted. Having observed these phenomena, one then has this thought: such volitional formations are truly impermanent in nature. The rest is as explained before. How does one observe the impermanent nature of the transformation of food matters (bhojana-vastu)? One observes various kinds of food and drink: at one moment they are not yet prepared, at another moment they are prepared; at one moment they enter the mouth and are chewed by the teeth, mixed with saliva and swallowed bit by bit; at another moment the food enters the belly and is gradually digested, and then is transformed into feces and urine and excreted. Having observed these phenomena, one then has this thought: such volitional formations are truly impermanent in nature. The rest is as explained before.