How is Dr. Mortimer inquisitive?

Dr. Mortimer is interested in the manuscript.

“The exact date is 1742.” Dr. Mortimer drew it from his breast-pocket. “This family paper was committed to my care by Sir Charles Baskerville, whose sudden and tragic death some three months ago created so much excitement in Devonshire. I may say that I was his personal friend as well as his medical attendant. He was a strong-minded man, sir, shrewd, practical, and as unimaginative as I am myself. Yet he took this document very seriously, and his mind was prepared for just such an end as did eventually overtake him.”

"Dr. Mortimer looked at Holmes with an air of professional interest..."