The Adventure of the Norwood Builder: Mistreatment
By the third time Holmes starved himself into unconsciousness I was no longer surprised, but the visceral fear caused by watching him crumple motionless to the floor remained as powerful as ever.
When he woke, I told him the truth.
"Your heart may be strong enough for this mistreatment, but mine is not."
I waited. The fourth occurrence never came.