The plaintiff has no valid ground of exception to the ruling of the court. The evidence did not show any act by the defendant which avoided his lease from the plaintiff. It is only a tenant or occupant who uses demised premises for unlawful purposes that forfeits his right or title to continue in *290the possession and use of “a building, place or tenement,” under Gen. Sts. c. 87, §§ 6 and 8. Nothing appeared at the trial from which any improper or unlawful use of the premises by the defendant could be inferred. On the contrary, the jury have found under the instructions of the court that any such use of the house was without the knowledge or consent of the defendant. His right to underlet a portion of the premises is not disputed. The statute does not make his right to occupy depend on the acts or conduct of his undertenant of which he had no knowledge. Healy v. Trant, 15 Gray, 312. Exceptions overruled.