RECENT years have brought forth an impressive wealth of new knowledge of the physiology of the subcortical structures of the brain. One of the most coherent and outstanding studies in this field is the experimental work of Prof. W. R. Hess, of Zurich. Unfortunately, none of Hess's publications have been translated, and it was felt, therefore, than an English summary of his studies on the autonomic function of the diencephalon deserved publication. The following summary was undertaken on the advice of many English-speaking neurologists and neurophysiologists who emphasized this need. The central problem of Professor Hess's work was that of the functional organization of the diencephalon, which was investigated mainly by electrical stimulation in the unanesthetized animal. This method shows the positive aspect of the function of this structure. The lesion method, very commonly used elsewhere, has some shortcomings, due in part to the fact that after a lesion not