Abstract
In an attempt to note the extent and to find the limits of certain suspected physiological changes produced during periods of prolonged mental effort, several series of carefully planned experiments were undertaken involving 3 subjects familiar with the solution of mental arithmetic problems. The task was uniform throughout and consisted in the solution of multiplication of 4 numbers by 4 numbers from memory alone. The level of metabolic rate was measured by oxygen consumption using the Graphic Metabolism machine. Changes in the blood elements, erythrocytes and leucocytes and changes in hemoglobin content were checked in the usual manner by use of the hemocytometer and the hemoglobinometer. Conspicuous changes in excretory products were determined by routine urine analyses, involving variations in specific gravity, reaction, occurrence of albumin and sugar, di-acetic acid and acetone. Five specific tests were made on each of the subjects, the first series to establish the “norms” without mental effort. Th...
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