One reference work states: “To take enough willow bark to achieve the benefits aspirin provides or to take enough foxglove to achieve the full lifesaving effects of digitalis is much more easily accomplished via a pill than by eating natural substances. ”
इन क्रियाशील यौगिकों को जब पेड़ों की छाल से निकाला जाता है तो उनकी पूरी - पूरी खुराक, एकदम सही मात्रा में दी जा सकती है ।