शीतोष्णस्निग्धरूक्षाद्यैरुपक्रान्ताश्च ये गदाः| सम्यक् साध्या न सिध्यन्ति रक्तजांस्तान् विभावयेत् ||१७||
The diseases, which, in spite of being curable, are not alleviated after treatment with any of six therapies like cold-hot, unctuous-rough etc. should be considered as caused by (impure) blood.
बलदोषप्रमाणाद्वा विशुद्ध्या रुधिरस्य वा| रुधिरं स्रावयेज्जन्तोराशयं प्रसमीक्ष्य वा ||१९||
[Extent of bloodletting] Bloodletting should be done considering the strength of the person, dosha, location of the disease, and until pure blood starts to flow out.
अरुणाभं भवेद्वाताद्विशदं फेनिलं तनु| पित्तात् पीतासितं रक्तं स्त्यायत्यौष्ण्याच्चिरेण च ||२०||
[Dosha-specific features of vitiated blood] Due to vitiated vata, blood becomes arunabham (reddish), non-slimy, frothy and thin. Due to vitiated pitta, it becomes yellow or blackish, with delayed coagulation because of heat.