50 ORGANISM AND ENVIRONMENT 
thought that the teleological significance at any rate is 
clear enough, since lowering of alveolar CO, pres- 
sure means raising of the oxygen pressure, thus com- 
pensating to some extent for any want of oxygen 
caused by the lowered oxygen pressure. But there 
may be no evident signs of want of oxygen, and lower- 
ing of alveolar CO, pressure is in itself a very dis- 
turbing influence, as has already been shown. When 
we first observed the persistent lowering of alveolar 
CO, pressure in connection with shorter experiments 
in a steel chamber we thought that lactic acid must 
have been formed in consequence of oxygen want, and 
that the persistence of the lowered alveolar CO, 
pressure after the experiment was due to lactic acid 
remaining in the body. But further observations by 
Boycott and Ryffel failed to confirm this theory ; and 
the persistence observed after longer observations in 
the chamber, and stays in the Alps, was far too great 
to justify the lactic acid theory. As already men- 
tioned the excess of lactic acid produced by muscular 
work disappears from the blood within about an hour. 
Barcroft meanwhile found on the Peak of Teneriffe 
that the dissociation curve of the oxyhaemoglobin in 
human blood was displaced to the right if the deter- 
mination is made in presence of 40 mm. pressure of 
CO, (that of the alveolar air at sea level), but was 
normal if made in presence of the existing lowered 
alveolar CO, pressure. From this it could be con- 
cluded that there is no appreciable change in the 
reaction of the arterial blood within the body at the 
higher altitude. The lowered alveolar CO, pressure 
