I was walking at a rapid pace up the avenue one raw, fall evening, when somewhere near the corner of Fifty--Street I was brought to a sudden stand-still by the sound of a child's voice accosting me from the stoop of one of the handsome houses I was then passing. "O sir " it cried, "please come in. Please come to grandpa. He's sick and wants you." Surprised, for I knew no one on the block, I glanced up and saw bending from the open doorway the trembling...