Experiments designed to identify the "origin of the contraction wave in the mammalian heart." Three photographic plates depict numerous electrocardiographic recordings. "From 1910 to 1916, Lewis and his associates performed classic experiments in which they outlined the sequence of electric activation of the heart." Burch 135. Citing this research, Arthur Hollman notes "Lewis was now at the peak of his electrophysiological studies which aimed to show the electrical events underlying cardiac contraction and his experimental work was remarkable for its scope and technical virtuosity" (Arthur Hollman, Sir Thomas Lewis, London, 1997, 58-60.)
Digital facsimile from the Royal Society at this link.