READJUSTMENTS OF REGULATION 43 



On studying more closely the effects of breathing 

 air very deficient in oxygen we found that the alveolar 

 CO 2 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 2 

 in the blood and lymph the alveolar CO 2 cannot be set 

 at once to the new level without evident panting. 

 When once the reserve of CO 2 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 2 

 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 2 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 



