One of the earliest studies on limb blood flow, using a volume plethysmograph to enclose the hand and forearm, was carried out by Hewlett and Van Zwaluwenburg (1909). Two of their patients were pronounced neurasthenics “with labile vasomotor systems” and these authors noted that, excluding subjects with thyrotoxicosis, “the majority of the remaining fast rates occurred in neurasthenics of the vasomotor type”. In 1938 Grant and Pearson, who developed forearm plethysmography to determine blood flow mainly in the skeletal muscle rather than the skin, noted transient increases in forearm flow with mental arithmetic in some subjects, but did not pursue this observation further. This response was studied in more detail by Abramson and Ferris (1940). Their conclusion that mental arithmetic produced an increase in forearm flow due to vasodilatation in the forearm muscles was confirmed by the work of Brod, Fencl, Hejl, and Jirka (1959), who attributed the change to emotional stress.