The observations related in this article were undertaken after reading the recent articles published in this journal by Barringer1 in which he describes a method used by him to estimate the capacity of the heart in normal and diseased subjects. The work has been done at the Hampstead Military Hospital, London, which institution has been set aside by the British War Office for the investigation and treatment of soldiers suffering from cardiac disabilities. After reading Barringer's article it seemed probable that we might find some qualitative difference between the blood pressure reaction following given test exercises, in healthy subjects and in those patients who form the greatest part of our material, namely, soldiers who suffer from the condition described as "irritable heart"; and that if such a difference could be discovered it would form a valuable help in sorting our patients for treatment. We have completed this comparison