102 



RESPIRATION 



more soluble in the tissues and lymph than in water. They have 

 thus practically no power of storing free oxygen. In the course of 

 our investigations on the effects of want of oxygen it became 

 evident that the center works very jerkily when excited by want 

 of oxygen, and the subject was studied in further detail by Doug- 

 las and myself. 15 We found that the effects of regulation of the 

 center by oxygen want could be observed very conveniently at 

 the end of the apnoea caused by forced breathing of ordinary air. 

 When apnoea is produced by forced breathing of air for about 

 two minutes, the oxygen percentage in the lungs runs down very 

 low before the pressure of CO 2 in the respiratory center has nearly 

 risen to its normal value. In some subjects there is an alarming 



fr-4 



VK. Mf 



mv.'i\Mi'.',lr, 



Figure 35. 



Variations in alveolar gas pressures after forced breathing 

 for two minutes. Thin line = oxygen pressure, thick line = CO 2 

 pressure. Double line = normal alveolar CO 2 pressure. The 

 actual breathing is indicated at the lower part of the figure. 



appearance of blueness in the face before any desire to breathe is 

 felt. Ultimately, however, the stimulus of oxygen want (together 

 with the subliminal CO 2 stimulus) suffices to start the breathing. 

 But the first four or five breaths greatly raise the alveolar oxygen 

 percentage and thus quiet the center down again, so that apnoea 

 again follows, which is again followed by breathing and subse- 

 quent apnoea, this periodic rising and dying away of the breath- 

 ing going on for about five minutes, as shown in Figure 34, though 

 not all subjects react alike. 



Figure 35 shows the variations of the alveolar oxygen and CO 2 



"Douglas and Haldane, Journ. of PAysiol., XXXVIII, p. 401, 1909. 



