THE BLOOD GASES 



337 



partial pressure in the alveoli. A storage of oxygen in the tissues does not 

 take place under such circumstances (Falloise, Durig). 



Neither does the absorption of oxygen suffer any change in consequence 

 of a fall in the partial pressure to 86 mm. or Iqwer. Only when the atmos- 

 pheric pressure sinks to 380 mm. (partial pressure of oxygen, 80 mm.) does 

 a decline in the oxygen content of the blood become evident; at a partial 

 pressure of 55 mm. the decline is marked (Loewy). 



The absorption of oxygen becomes less as the carbon-dioxide tension in the 

 blood increases. At an oxygen tension of 50 mm. Hg. and a carbon-dioxide 

 tension of 5 mm., the absorption of oxygen was ninety-three per cent ; with the 



FIG. 131. The absorption of oxygen by horse's blood, after Krogh. The abscissae represent the 

 partial pressures of oxygen and the ordinates percentages of saturation. 



same oxygen tension and a carbon-dioxide tension of 40 mm. it was seventy- 

 eight per cent. As the blood flows through the capillaries the oxygen is gradu- 

 ally used up and at the same time the carbon-dioxide tension increases ; the lat- 

 ter has the effect of conferring a greater tension on the oxygen present, as a 

 consequence of which a larger quantity of oxygen can be placed at the disposal 

 of the tissues. The influence of this factor is especially great in asphyxiation 

 (Bohr, Hasselbach and Krogh). 



C. CARBON DIOXIDE 



Where carbon dioxide occurs in the blood and how it is combined are 

 much more complicated questions than in the case of oxygen, and notwith- 

 standing many investigations directed to this end, the matter is not to be 



