WE have now concluded our review of the principal schools which have played such a great part in twentieth-century psychology. It will have been noticed that sensation, which figures so largely in the earlier days of experimentalism, receives as a rule but little attention in the special lines of research that distinguish the different schools and in the matters in dispute between them. And, indeed, with the devising of fresh methods, able to cope with the "higher processes" in an accurate and systematic way, it was inevitable that interest should largely be deflected from the "gateways of knowledge" to knowledge itself, and to the other aspects of the mind that show, at best, but an indirect dependence on the senses. Nevertheless, a very considerable amount of work continued to be done in the psychology and physiology of sensation, though relatively to the whole, this amount is vastly less than in our second period. In direction, too, it is somewhat changed; for, as was perhaps to be expected, the most important discoveries have been made in those sense departments as regards which comparatively little progress had been made before. We may briefly indicate a very few of these developments.
We have seen how, in the field of cutaneous sensation, a new era began with the discovery of "spots" in 1884. Another period may be said to have begun in 1911, following an experiment which Head performed upon himself, in the hope of throwing light upon some anomalies of sensation that he had observed among his patients. The radial and external