Ashtangasamgraha 37.2

37.2

trividhā hi gatiḥ śalyānāmūrdhvamadhastiryak ca |

sā punaḥ pratyekamṛjuvakrabhedena dvividhā ||

yavakṣāraśuktisaurāṣṭrīkalkaiśca lepayet ||

For the course of foreign bodies is threefold: upward, downward, and oblique.
Moreover, each of these is twofold, according to whether it is straight or crooked.
And one should apply a paste of barley alkali, pearl oyster shell, and saurāṣṭrī.