A Contribution to the Physiology of Sleep, Based upon Plethysmographic Experiments

The primary object of these experiments was to determine the variations in volume of the arm as measured by a water plethysmo= graph during the entire period of normal sleep. The experiments were begun some years ago by Messrs. Bardeen and Nichols, who wer~ at that time students in this laboratory. Their work gave them some very interesting curves, showing the sensitiveness of the vaso-motor centre to sensory stimuli not sufficiently strong to awake the subject experimented on, but they were unable to obtain a satisfactory plethysmographic record of an entire sleep period. This latter point I have endeavored Co co~nple~e by experiments made upon myself at various times within the last few years. At first a large plethysmograph was used, measuring the changes in volume of nearly the entire arm; but this was afterwards abandoned, owing to the fact that the arrangements used to ensure immobility necessarily kept the arm in full extension, a position that quickly caused painful discomfort at the elbow joint and thus prevented normal sleep. The plethysmograph used in all the experiments here reported was much smaller, measuring the volume changes only in the hand and the lower part of the fore-arm, and allowing comfortable flexion and freedom of movement at the elbow. The apparatus employed was simple in character and can be sufficiently understood from a brief description.