RESPIRATION 



119 



effects of excess of CO2 and anoxaemia are combined there is 

 great increase of both depth and frequency, so that far more air is 

 breathed than when either excess of CO2 alone, or anoxaemia 

 alone, is the stimulus. In my own case, for instance, when the 

 breathing was pushed, in short experiments, to as much as seemed 

 bearable, 131 liters per minute, with a depth of 1.98 liters and a 

 frequency of 66 per minute, were breathed when the effects of 

 excess of CO2 and anoxaemia were combined; and only 81 liters, 

 with a depth of 2.69 and a frequency of 30, when the only stimulus 

 was excess of CO2. 



Figure 39 shows quantitatively the effects of rebreathing a 

 small volume (about 2 liters) of air or oxygen from the recording 

 concertina already described. It will be seen that the increase in 

 frequency was much less when the effects of anoxaemia were cut 

 out by the oxygen. 



Figure 40 A shows the effect on the same subject of similar re- 

 breathing when the accumulation of CO2 was prevented by inter- 



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Figure 40. 

 Rebreathing through soda-lime from concertina. Time-marker = 2 seconds, 

 (a) Subject Cpl. M. (b) Subject J. S. H. 



posing a layer of soda lime. It will be seen that the frequency 

 increases, but not the depth. Figure 40 B shows the effects on 

 another subject, whose respiratory center responds much more 

 readily to the effects of anoxaemia. In this case depth as well as 

 frequency are considerably increased. It must, however, be borne 

 in mind that, in short experiments such as these, the increased 

 breathing, as already explained, is mainly due to the necessity of 



