Agni (digestive fire)

The introduction says agni here means the digestive fire, which is of four kinds, weak (manda), sharp (tīkṣṇa), irregular (viṣama) and balanced (sama), and that balanced agni is the best.

Besides balanced fire, disordered digestive fire is described in three kinds arising from aggravation of the doshas: irregular (viṣamāgni), sharp (tīkṣṇāgni) and weak (mandāgni).

For people in youth, middle age and old age too, the physician should carefully consider, according to the texts, whether the digestive fire is balanced, irregular or weak, and give suitable treatment.

The eight great procedures (oleation, sudation, emesis, purgation, oil enema, decoction enema, bloodletting and head purgation) are said to make the abdominal fire weak; it should then be raised with fire-increasing water and foods, as a careful person builds a tiny spark into a fire step by step with fine dry grass and wood.

The introduction says the digestion of the six tastes of food just eaten stimulates the pācaka pitta; in the āmāśaya the pācaka pitta and the kledaka kapha are released and gradually mix with the food, which then undergoes vipāka. It says the digestion of food takes about four to six hours and goes on in the āmāśaya, pakvāśaya and grahaṇī.

In indigestion the digestive fire is described as so weak that it cannot digest food, medicine or the doshas, which is why fasting is advised.