Identify: The back door to the laboratory

From the text:

 "Two doors from one corner, on the left hand going east the line was broken by the entry of a court; and just at that point a certain sinister block of building thrust forward its gable on the street.  It was two storeys high; showed no window, nothing but a door on the lower storey and a blind forehead of discoloured wall on the upper; and bore in every feature, the marks of prolonged and sordid negligence.  The door, which was equipped with neither bell nor knocker, was blistered and distained."