Investigation of spontaneous vasomotor activity. Relation of the sympathetic and somatic nervous systems to the occurrence of slow waves (alpha and beta) of the plethysmogram of the dog's paw.

OF THE 5 different waves described as appearing in the normal plethysmogram of an extremity, the last 3 (alpha, beta, and gamma waves) are grouped together as the slow or third order waves. Their relative frequencies in the human digit are 2 to 14 per minute, 1 to 2 per minute, and 1 to 8 per hour. They were first described by Hewlett and Van Zwaluwenberg (1909) as large vasomotor waves "evidently due to marked vasomotor instability." Since then, these slow waves have been seen in the human digit,' forehead skin, nasal septum, and the pinna of the ear. Hargis and Mann (1925),° in plethysmographie studies of the spleen in unanesthetized dogs, reported third order waves which resemble the slow waves of the digital plethysmogram. These were present after denervation of the spleen. Also described was a "splenic reflex" to sensory stimuli (noise, pain) which very much resembles the digital vasoconstrictor response. This was abolished by denervation. In addition, we have seen slow waves in plethysmograms recorded from the subarachnoid space; this area a'so shows a vasoconstrictor response to sensory stimuli. Burton (1939) carried out plethysmographie studies on one patient after unilateral cervical ganglionectomy (presumably this was a cervical approach to the stellate ganglion) and reported little correspondence be-