REGULATION OF RESPIRATORY MOVEMENTS 1205 



question arises, which, of these two changes is responsible for the 

 different physiological events which characterise asphyxia ? At 

 various times these phenomena have been ascribed either to the 

 increased tension of carbon dioxide or to the diminished tension of 

 oxygen in the centre. The view that the normal stimulus to the 

 respiratory centre in asphyxia was the lack of sufficient oxygen and 

 that the normal activity of this centre was determined by the tension 

 of oxygen in the blood circulating through the brain was first put 

 forward by Rosenthal. When sufficient oxygen was present, the 

 centre, according to this observer, would cease to act, so that a condi- 



FIG. 503. Effect of C0 2 on respiratory movements of rabbit. (SCOTT.) 

 Upper line, tracing of diaphragm slip (Head's method). Lower tracing, 

 carotid blood pressure. During the first period indicated on the signal line 

 the animal breathed 9' 6 per cent. C0 2 in air, and during the second period 

 10 per cent. C0 2 with 33 per cent, oxygen. Time tracing = 2 sees. Scale = 

 mm. Hg. blood pressure. 



tion of apnoea would be produced. According to Traube, on the 

 other hand, the special respiratory stimulus was the excess of carbon 

 dioxide in the blood, and this view was supported strongly by Miescher. 

 The tendency of recent work, especially by Haldane and his pupils, 

 has been to show that there is an element of truth in both views 

 that indeed the respiratory centre can be excited either by excess 

 of carbon dioxide or by lack of oxygen, but that its sensitivity to 

 carbon dioxide is by far the most important factor in the determination 

 of the increased respiratory movements in asphyxia, and is the only 

 chemical factor which can be regarded as playing any part in the 

 regulation of the respiratory movements under normal conditions. 

 This factor is well brought out if we investigate the effect on the 

 respiratory movements of altering the tensions of the two gases in the 

 air breathed. If by this means we succeed in altering the tension of 

 the two gases in the alveolar air we rday assume that the tensions 

 of the gases in the arterial blood leaving the lungs are altered in the 



