332 RESPIRATORY FUNCTION OF THE BLOOD 



CO free 1 

 free COg in order to preserve this ratio -, = . That 



CO2 combined 20 



is, the CO2 tension in the muscle capillaries tends to increase, 

 and increase of COg tension causes increased unloading of oxygen 

 from oxy-haemoglobin. 



Increased activity postulates increased energy usage, which renders 

 necessary an immediately increased supply of oxygen. The amount 

 of oxygen required is liberated by the desaturating action of CO^ — the 

 inain chemical product of the activity. 



The amount of oxygen in the blood does not control oxidation 

 in the tissues, but the call for oxygen by the tissues controls the 

 rate of unloading of oxygen. 



Transport oJ carbon-dioxide. 



The principle underlying the transport of carbon-dioxide is 

 identical with that enunciated for oxygen. In the tissues the 

 tension of carbon-dioxide is relatively high and the gas passes to 

 the blood, is carried to the lungs, and is there eliminated. The 

 erythrocyte, once freed from its load of oxygen, takes on a cargo of 

 carbon-dioxide. Part of this cargo is carried by the haemoglobin 

 and part is dissolved in the corpuscular lipoid envelope causing it 

 to swell. Lipoid is capable of dissolving very large amounts of 

 COo. But the erythrocytes are not the sole means of transport. 

 Carbon-dioxide is about twenty-five times as soluble in water 

 as oxygen under similar conditions. Relatively more COg will, 

 therefore, be carried in true solution in the plasma. In addition 

 to this amount (which we have just seen is carefully regulated) a 

 considerable quantity of the gas is adsorbed to the various colloids 

 of the plasma, (i.) Each gram of fibrinogen can carry 1/30 gram 

 of CO2. (ii.) Serum proteins may adsorb a measurable quantity of 

 carbon-dioxide — at the lowest estimate, over 5 per cent. It is 

 obvious that while these factors may almost be neglected in the 

 consideration of the transport of oxygen, they have to be reckoned 

 with in the case of carbon-dioxide. 



TABLE XLVIIT 



Partition op Co, in 100 c.c. of Depibrinated Blood 

 (Haematocrite Value = 51) 



That is, in arterial (whole) blood there is about 50 c.c. of COg, 

 of which amount the fibrinogen carries about 5 c.c, the serum 



