In A Search in Secret India, I described the case of a hatha yogi whose heart appeared to stop at will. Several years later a French physician travelled to India, bringing with him certain scientific instruments with which to investigate yogic powers. Another yogi known to me was examined by the doctor and the electric cardiograph was applied to the yogi's heart after it had apparently ceased to function. The result on the instrument showed that the heartbeat was extremely slow, but quite perceptible beating still continued. Thus, the evidence of unaided sight and touch on the part of the observer was actually refuted by the accurate findings of a delicate instrument.
-- Notebooks Category 12: Reflections > Chapter 5: The Literary Work > # 197