Is Breathing Fundamentally a Reflex Phenomenon?

IT has been long assumed, but it is still uncertain, that the so-called respiratory centre possesses independent automaticity. On the other hand, there is abundant evidence of the importance of reflex control of respiratory movements. Whether the rhythmic discharge of the respiratory centre will eventually prove to be a localised physicochemical process [Gesell, 1925] in and about a group of neurones on the motor side of the respiratory neurone chain which is modified by afferent nerve impulses, or whether it will prove to be fundamentally a reflex phenomenon [Schaffer, 1932; Gesell and Moyer, 1935] modified by chemical conditions along the respiratory reflex arcs, is the primary question raised by the present paper. The adjustment of pulmonary ventilation by chemical stimulation of sensory nerve fibres ending in the carotid gland, demonstrated by Heymans [1927], and now abundantly confirmed, gives emphasis to the reflex mechanism of control. The stimulation by carbon dioxide after sinus denervation and double vagotomy [Heymans, 1927], the effects of arterial injection (Na2Co3, NaHCO3, NaCN, and Na2S) beyond the carotid gland [Owen and Gesell, 1931; Winder, Winder and Gesell, 1933; Winder and XWinder, 1933], and the stimulation of respiration from painting the floor of the fourth ventricle with NaCN and Na2S. (Owen and Gesell [1931], however, force us to give due consideration to the possibility of a direct chemical action on the respiratory centre itself. But until we have a more complete explanation of these effects the question of direct central chemical action versus reflex chemical stimulation will remain unanswered for reflex endings susceptible to chemical stimulation, quite obviously may exist within the brain itself. If such endings do exist, but for the time cannot be demonstrated, the solution of the control of respiration will be difficult indeed. The situation w-ill be comparable to that existing before the opportune discovery of the rifle of the carotid gland by Heymans. Several years ago, when we were looking for new leads on the