READJUSTMENTS OF REGULATION 43 
On studying more closely the effects of breathing 
air very deficient in oxygen we found that the alveolar 
CO, pressure still regulates the breathing; but the 
regulation is, as it were, set at a lower level. The 
great panting produced at first by want of oxygen is 
due to the fact that owing to the large reserve of CO, 
in the blood and lymph the alveolar CO, cannot be set 
at once to the new level without evident panting. 
When once the reserve of CO, has been got rid of, the 
breathing diminishes, while the blueness and other 
symptoms increase. If the oxygen percentage or pres- 
sure in the air is only diminished gradually there is no 
evident panting, although there is still some increase in 
the breathing, as shown by the lower alveolar CO, 
pressure. The formidable symptoms come on without 
the warning given by panting. Nevertheless. apnoea 
can still be produced easily enough by forced breathing 
sufficient to reduce the alveolar CO, pressure further, 
even though the face is blue all the time, and con- 
sciousness fails before there is any desire to breathe. 
It was through attending too exclusively to want of 
oxygen as a cause of the “venosity” of the blood that 
so many mistakes were made by physiologists as to 
the causes of apnoea, and the general physiology of 
breathing. 
The action of gradually developing want of oxygen 
is very insidious, until dangerous effects develop with 
dramatic suddenness. These effects have been 
repeatedly observed by balloonists, as well as in mines. 
Nothing illustrates the effects better than the experi- 
ences of the well-known meteorologist Glaisher and his 
