What is Stamford's warning about Holmes?

Answer 1

Of the many things Stamford says about Holmes, this is probably what you are asking about:

"It is not easy to express the inexpressible," he answered with a laugh. "Holmes is a little too scientific for my tastes - it approaches to cold-bloodedness. I could imagine his giving a friend a little pinch of the latest vegetable alkaloid, not out of malevolence, you understand, but simply out of a spirit of inquiry in order to have an accurate idea of the effects. To do him justice, I think that he would take it himself with the same readiness. He appears to have a passion for definite and exact knowledge."