RESPIRATION • 135 



tambour the movement of which, as shown, closes a circuit from 

 an accumulator or from the lighting circuit through a rheostat. 

 This circuit passes through an electromagnet which instantly 

 lifts a valve and admits air freely into the concertina, which at 

 once refills itself. At the end of expiration the circuit is instantly 

 broken and the valve closes, so that only the volume of air 

 contained in the concertina can be inspired at the next inspiration. 

 In this way the amount of air taken in per breath can be limited, 

 and a continuous record is at the same time obtained of the depth 

 and frequency of respiration. With the concertina fully open 

 ordinary records of the breathing are obtained, and any gaseous 

 mixture can be supplied through a glass cylinder which incloses 

 the electromagnet and valve. The advantage of this method is 

 that it is capable, not merely of permitting a study of shallow 

 breathing, but also of giving a continuous quantitative record of 

 any sort of breathing. The old stethographic method of recording 

 the breathing is apt to be misleading, since it does not give a 

 quantitative record. 



When the depth of inspiration is limited by means of this ap- 

 paratus the natural impulse, at first, is to continue the inspiratory 

 effort at the end of each inspiration, as the Hering-Breuer reflex 

 has not given the signal for expiration. With a little practice, 

 however, the breathing goes quite easily, and the frequency in- 

 creases in proportion as the depth is diminished. When the depth 

 is greatly limited the breathing becomes very frequent — 100 or 

 more a minute. 



On observing the breathing when the depth was gradually more 

 and more limited, we found that the breathing became periodic 

 very readily. As already explained, periodic breathing is a symp- 

 tom of anoxaemia, and this fact led us to try the effect of adding 

 a little oxygen to the inspired air. This promptly abolished the 

 periodic breathing, as shown in Figure 44. There could thus be 

 no doubt that the periodic breathing was due to imperfect oxy- 

 genation of the arterial blood. In some persons, such as myself, 

 the periodic breathing was produced much more readily, and in a 

 more striking degree, than in other persons. This, as already 

 mentioned in Chapter VI, is due to individual differences in the 

 response of the respiratory center to anoxaemia. 



We at first thought that the anoxaemia must be due to the fresh 

 air not penetrating properly to the deep (air-sac) alveoli when 

 the breathing was shallow; but on examining samples of the deep 

 alveolar air during a prolonged experiment, we were disappointed 



