What does Poole show him regarding communications from Jekyll to the local chemists?

Utterson reasons that if someone murdered Jekyll, he would not still be in the house. Poole explains that the man, or "whatever it is," has been begging for a specific sort of medicine, "night after night." Before apparently disappearing, Jekyll had also been searching for a specific medicine, and would write his orders down and pass them under the door to Poole. Following his master's orders, Poole searched high and low for the medicine, but everything he has brought back has been deemed useless or impure. Utterson asks to see a written request, and Poole produces one from his pocket. The note seems quite professional, expresses a sense of urgency, and then falls into desperation: "For God's sake, find me some of the old [drug]."