28 RESPIRATION 



mained constant, since increased or diminished depth of breathing 

 compensated for diminished or increased frequency. The manner 

 in which this correspondence between depth and frequency is 

 brought about will be discussed in the next chapter. 



During any considerable muscular exertion the discharge of 

 CO 2 from the lungs is enormously increased ; and in view of the 

 facts already described we should expect to find the breathing 

 similarly increased, with a rise in the alveolar CO 2 percentage 

 corresponding to the rise observed when the breathing is corre- 

 spondingly increased by breathing air containing an excess of 

 CO 2 . Priestley and I obtained the following mean results during 

 work on a somewhat primitive bicycle ergometer. 



In this series there was thus only a mean rise of 0.285 per cent 

 in the alveolar CO 2 , whereas we had expected to find a rise of 

 about 0.6. The correspondence was, however, in the right direc- 

 tion, and we endeavored, mistakenly as afterwards appeared, to 

 explain the lack of exact correspondence. 



A more complete series was carried out later with much im- 

 proved apparatus by Douglas and myself, with Douglas as sub- 

 ject. 12 The accompanying table shows the data for volume of air 

 breathed, oxygen consumed, CO 2 given off, composition of ex- 

 pired air, and of alveolar air. In these experiments we used the 

 now well-known bag method of Douglas for determining the 

 respiratory exchange. 13 



It will be seen from this table that with a CO 2 production in- 

 creased from 264 cc. per minute during rest standing to 1398 cc. 

 per minute during walking at 4 miles on grass the alveolar CO 2 

 percentage rose from 5.70 to 6.36, i.e., by 0.66 per cent. The vol- 

 ume of air breathed per minute was increased from 10.4 to 37.3, 



u Douglas and Haldane, Journ. of Physiol., XLV, p. 235, 1912. 

 "Douglas, Journ. of Physwl., XLII, Proc. Physiol. Soc., p. xvii, 1911. 



