838 RESPIRATORY FUNCTION OF THE BLOOD 



respiratory carbon-dioxide, it is obvious that some other factor 

 must be involved which determines how much carbon-dioxide 

 shall enter the red corpuscle and how much shall react with 

 chloride in the plasma, liberating hydrochloric acid, which then 

 enters the red cell. 



Since the passage of carbon-dioxide into the cell under increased 

 carbon-dioxide tensions, and the passage of carbon-dioxide out of 

 the cell under lowered carbon-dioxide tensions, is accompanied by a 

 transfer of chlorides in the same direction, it would seem that the 

 distribution of one of these electrolytes is related to the distribution 

 of the other. For information on this point, the distribution of all 

 the main solutes of the blood between plasma and cells must be 

 studied. It is then found that : — ■ 



(1) The solutes of the blood are so distributed that the red cell 

 contents and plasma are isotonic (q.v.). This is indicated by the 

 shape of the cells (Chap, XXII,). 



(2) The red cells are impermeable under physiological conditions 

 to the bases of the blood (excepting the hydrion), 



(3) The red cells are freely permeable to the non-colloidal 

 anions of the blood, 



(4) The red cells are impermeable to the protein anions of the 

 cells and plasma. 



From Donnan's theory of membrane equilibria (q.v.) it may be 

 deduced that under these four conditions, for thermodynamic 

 equilibrium 



[Cy _ [HCO3J _ [HJ _ [AJ 



[CIJ [HCO3J [HJ [AJ 



Where [AJ is the ionic concentration of anions in the cell. 



[A J is the ionic concentration of anions in the serum, etc. 



[A 1 

 The ratio — ^ has been called r. 



[AJ 

 Thus it is seen that when carbon-dioxide enters the blood, thus 



riTCO 1 



altering the ratio '—, a re-distribution of the other mono- 



[HCO3J' 



valent anions (mainly chlorides) must occur to preserve thermo- 

 dynamic equilibrium. But this is not the only condition governing 

 the electrolyte distribution in blood. For osmotic equilibrium the 

 total osmolar concentration in plasma and cells must be equal, and 

 therefore the passage of carbon-dioxide and chloride from plasma 

 to cells must be accompanied by a passage of water in the same 

 direction, with a consequent increase in cell volume. Also for 

 electrical equilibrium the total positive ions of the serum must equal 



