The question in controversy, and upon which both parties had introduced the testimony of experts, was whether the injury to the plaintiff’s house was caused by the fumes and gases from the defendant’s works, or by the emanations from a sewer. The grounds and reasons of the opinions of the experts, including the détails of experiments made by them under conditions and circumstances which, as they testified, were as nearly as possible like those surrounding the plaintiff’s house in the absence of the sewer, were rightly permitted to be stated by the experts, in order to assist the jury in understanding their testimony and applying it to the case. Lincoln v. Taunton Copper Co. 9 Allen, 181. Commonwealth v. Piper, 120 Mass. 185, 190. Williams v. Taunton, 125 Mass. 34. Exceptions overruled.