MODE OF ACTION OF RESPIRATORY STIMULANTS: I. MODE OF ACTION OF OXYGEN LACK

¹ Department of Physiology, Middlesex Hospital

(1) The effects on respiration of inhalation of various concentrations of oxygen (ranging from 4 to 16 per cent.) and of nitrogen has been studied in the decerebrate cat and in the chloralosed animal.

(2) With the sinus nerves and vagi eliminated, oxygen lack acts as a depressant to the "isolated" respiratory centre. The increase in breathing which is frequently obtained in the intact animal is wholly reflex, and depenads on excitatory afferent impulses in the sinus nerves and the vagi which overcome the direct depression of the centre which is simultaneously occurring.

(3) The reflex stimulation from the sinuses may, under certain circumstances, be of greater importance than that produced by the vagi.

(4) The integrity of the buffer nerves may enable the respiratory. centre to withstand for long periods degrees of anoxæmia which are lethal to it when it has been "isolated" by section of the vagi and denervation of the sinuses.

(5) The classical theories accounting for the stimulating action of oxygen lack are reviewed, and it is suggested that in the light of the fresh evidence they are no longer tenable. Anoxsemia decreases the response of the "isolated" respiratory centre to carbon dioxide.