860 RESPIRATION AND OXIDATION. 



In 100 cc. blood Oxygen taken up 



From the above table we see that even with an oxygen tension which 

 amounts to only one-half of the oxygen pressure in the air, the haemoglobin 

 is saturated in greatest part with oxygen. The dissociation is hence at 

 70-80 mm. pressure only slightly more than with a pressure of 150 mm. 

 and indeed even with as low a pressure as 40-30 mm., still 90-80 per cent 

 of the entire quantity of oxygen taken up chemically at 150 mm. is com- 

 bined with the haemoglobin. 



From these and other observations it follows that the oxygen partial 

 pressure may sink to one-half of that existing in the atmospheric air 

 without markedly influencing the oxygen content of the blood. This 

 also coincides with the experience of FRANKEL and GEPPERT 1 on the 

 action of low air pressures upon the oxygen content of the blood of dogs. 

 With an air pressure of 410 mm. Hg, they found that the oxygen content 

 of arterial blood was normal. With an air pressure of 378-365 mm. 

 it was slightly diminished, and only on reducing the pressure to 300 

 mm. was a noticeable decrease observed. A. LoEWY 2 found that 

 the lowest oxygen pressure of the alveolar air wherein the exchange 

 of material can go on normally both qualitatively and quantitatively, 

 is equal to 30 mm. Hg. 



In regard to the above-mentioned action of low air pressure it must 

 be remarked that the alveolar oxygen tension is regulated by changes 

 in the respiration, so that with great diminution in the quantity of oxygen 

 of the inspired air, the alveolar air contains the same quantity of oxygen 

 as with a higher oxygen partial pressure of the inspired air (LOEWY). 

 For example, LOEWY found the same quantity of oxygen, namely, 6.1 

 per cent, in the alveolar air with 16 and with 10.5 per cent oxygen in 

 the inspired air, because the respiration in the latter case was 8.5 liters 

 per minute against only 4.9 liters in the first case. 



It may be concluded from the large quantity of oxygen or oxyhsemo- 



1 Ueber die Wirkungen der verdiinnten Luft auf den Organismus, Berlin, 1883. 



2 A. Loewy, Untersuch. iiber die Respiration und Zirculation, etc., Berlin, 1895; 

 Centralbl. f. Physiol., 13, 449, and Arch. f. (Anat. u.) Physiol., 1900. 



