What is the practical application of this? In operative surgery there is introduced a new principle, which removes from surgery much of the immediate risk from its trauma by establishing ANOCI-ASSOCIATION; it places certain of the phenomena of fear on a physical basis; it explains to us the physical basis for the impairment of the entire individual under worry or misfortune; it makes evident the physical results of the daily noci-associations experienced by the individual as a social unit. On the other hand, it explains the power of therapeutic suggestion and of other influences which serve for the time to change the noci-integration; it shows the physical basis for the difference between hope and despair; it explains some of the phenomena of Graves' disease, of sexual neurasthenia, possibly of hay-fever and of the common cold. The principle is probably equally applicable to the acute infections, in each of which chemical noci-association gives rise to many of the phenomena of the disease and it explains their cure by natural immunity and by vaccines. This hypothesis should teach us to view our patients as a whole; and especially should it teach the surgeon gentleness. It should teach us that there is something more in surgery than mechanics, and something more in medicine than physical diagnosis and drugs. Conclusion The brain-cells have existed for eons and, amid the vicissitudes of change, they have persisted with perhaps less alteration than has the crust of the earth. Whether in man or in the lower animals, they are related to and obey the same general biologic laws, thus being bound to the entire past and performing their function in accordance with the law of phylogenetic association. For so long a time have we directed our attention to tumors, infections, and injuries that we have not sufficiently considered the vital force itself. We have viewed each anatomic and pathologic part as an entity and man as an isolated phenomenon in nature. May we not find in the laws of adaptation under natural selection, and of phylogenetic association, the master key that will disclose to us the explanation of many pathologic phenomena as they have already explained many normal phenomena? And may medicine not correlate the pathologic phenomena of the sick man with the forces of evolution, as the naturalists have correlated the phenomena of the sound man, and thus may not disease, as well as health, be given its evolutionary setting? PHYLOGENETIC ASSOCIATION IN RELATION TO THE EMOTIONS[*] [*] Address before the American Philosophical Society, Philadelphia, April 22, 1911.