268 RESPIRATION 



the oxygen 8.40 liters, the general mean being 8.4 liters. As my 

 pulse rate was 80 to 85 per minute this means that just about 100 

 cc. of blood were delivered at each heartbeat; and as my blood 

 volume is about 4.8 liters (see p. 280 of the Pike's Peak Expedi- 

 tion's Report) a volume of blood equal to that in the whole body 

 was passing round every 35 seconds. 



This is a much higher rate than has usually been calculated in 

 recent years, but not higher than what the data of Loewy and 

 von Schrotter indicate. There are so many sources of probable 

 error in the nitrous oxide method, 7 that I do not think that much 

 stress can be laid on the lower estimates which this method has 

 given during the resting condition. Nevertheless it is already 

 evident from our experiments that considerable individual dif- 

 ferences exist in the resting circulation rate in man; and it is 

 probable that under abnormal conditions both the circulation 

 rate and the delivery per beat vary considerably even in persons 

 of the same weight. 



At different times we have found very little difference in the 

 resting venous gas pressures of the same individual. These gas 

 pressures seem to be not much less steady during rest under 

 normal conditions than the arterial gas pressures. It is very dif- 

 ferent, however, during exertion. The smallest muscular exertion 

 raises the venous CO 2 pressure, and the rise is far more than 

 corresponds to the comparatively slight rise in arterial CO 2 pres- 

 sure as measured in the ordinary way in the alveolar air. Hence 

 it is now perfectly certain that the general circulation rate does 

 not increase in anything like direct proportion to increased me- 

 tabolism. Even with moderate exertion (about a third the maxi- 

 mum possible) on a Martin's ergometer, the difference between 

 arterial and venous CO 2 pressure became about two and one-half 

 times as great as usual, so that the venous blood could not be more 

 than about 45 per cent saturated with oxygen. So far as we can 

 calculate there is sometimes more increase in circulation than can 

 be accounted for by increased pulse rate ; but the increase is seldom 



7 For instance, it seems very probable that while the breath is held in perform- 

 ing an experiment the blood flow to the heart, and consequently through the lungs, 

 is temporarily diminished. Krogh and Lindhard, misled, as we believe, by the 

 imperfect mixture of oxygen in the alveolar air in their experiments, estimated that 

 there is a greatly increased absorption of oxygen, and a corresponding abnormal 

 increase in circulation, while the breath is held ; and their results are corrected 

 accordingly. The correction, which is a large one, does not seem to us to be war- 

 ranted, and without it their results come much closer to ours. This is especially 

 true for Lindhard's later results. 



