The concept of essential hypertension includes those cases of chronic hypertension which neither clinically nor anatomically can be demonstrated to have evolved from antecedent inflammatory disease of the kidneys or from urinary obstruction. The clinical picture of essential hypertension is, as a rule, quite distinctive, and has become widely known, in recent years, through the publications of Huchard,1 Janeway,2 Allbutt,3 Volhard4 and others, in their respective countries. As a result of these studies, it is now possible to diagnose essential hypertension with a fair degree of certainty in the large majority of cases. But we are occasionally confronted at necropsy by a secondary (i. e., postnephritic) contracted kidney, despite the fact that the clinical features of the case gave no indication that the hypertension was associated with inflammatory disease of the kidneys. Because of such rather exceptional cases, essential hypertension cannot be unequivocally defined by the absence of clinical evidence