There is no example of two agents so closely united as Mind and Body without some mutual interference taking place, and an increased knowledge of the workings of our bodies has vastly increased the knowledge of our mental actions, and will continue to do so more and more as we continue our researches. To confine ourselves to the study of the nervous substance would be to misrepresent the union, and the knowledge of that substance, however complete, would not suffice to solve the problem.