360 THE RESPIRATION 



a much longer period without any evident symptoms of hyperpnea, even 

 though the 2 percentage in the alveolar air may fall as low as in the 

 previous experiment, and there are marked symptoms of 2 want, such 

 as cyanosis, twitching of the muscles of the hands, lips, etc. The re- 

 spiratory quotient does not become abnormal in this experiment indicat- 

 ing that no excessive expulsion of C0 2 from the blood can have occurred as 

 in the previous experiment. The cause for the virtual abscence of hyper- 

 pnea in this experiment is no doubt that the more gradual reduction in 

 2 of the alveolar air and therefore of the blood did not bring about the 

 accumulation of lactic acid at a rate that was greater than that at which 

 the C0 2 was got rid of into the alveolar air. 



BREATHING IN RAREFIED AIR; MOUNTAIN SICKNESS 



In considering the part played by fixed organic acid in the control 

 of the C H of the blood, the most important results have been secured 

 by observations on the condition of individuals living at high altitudes. 

 As is well known, under these conditions certain symptoms are likely 

 to develop, the condition being known as mountain sickness. The great 

 interest which physiologists have taken in this subject has been owing, 

 not so much to the importance of the observations in connection with 

 the condition itself, as to the light which they throw on the mechanism 

 of respiratory control and on the cause for abnormal types of breathing. 



More or less hyperpnea, especially on exertion, soon appears in a 

 rarefied atmosphere, and the alveolar C0 2 tension assumes a value con- 

 siderably below the normal. For example, at sea level the minute vol- 

 ume of air breathed in one individual was 10.4 liters, and the alveolar 

 C0 2 tension 39.6 mm. Hg. After being some time on Pike's Peak, where 

 the barometer registers only 459 mm. Hg, Douglas 26 found the minute 

 volume of air to be 14.9 liters, and the alveolar C0 2 tension 27.1 mm. Hg. 

 At first sight the above statement may seem to contradict one pre- 

 viously made, to the effect that the alveolar C0 2 tension remains constant 

 at different barometric pressures. This applies, however, to the imme- 

 diate effects, whereas we are now considering the later effects. The im- 

 portant point is: How are we to reconcile with the above hypothesis the 

 fact that a diminution in the alveolar C0 2 tension should be accompanied 

 by hyperpnea? A solution of the seeming contradiction will not only 

 be of importance in connection with our present problem, but will assist 

 us in the investigation of the clinical conditions of hy'perpnea, in which 

 likewise a diminished C0 2 alveolar tension is often observed. Mountain 

 sickness may indeed lie considered as an intermediate condition between 

 the physiological and the pathological. 



From what we have learned we should expect the above result to be 



