Astanga Hrudaya
बहुपित्तो मृदुः कोष्ठः क्षीरेणापि विरिच्यते। प्रभूतमारुतः क्रूरः कृच्छ्राच्छ्यामादिकैरपि॥३४॥
A person with Mrudukoshta (soft intestines), even milk will induce purgation. For a person with Krurakoshta, (hard bowels, intestines), even Trivrit (a purgative herb) might cause purgation with great difficulty.
english translation