DOUGLAS M. SURGENOR 



the phagocytic action of the leukocytes, on the interactions of 

 specific antibodies, and on more diffuse, but nonetheless im- 

 portant, bactericidal properties of the plasma. Finally, the blood 

 is endowed with facilities for the maintenance of its own integ- 

 rity, both with respect to its aqueous content and fluidity 

 and also to loss through openings in the blood vessels. The 

 elucidation of the biochemical mechanisms of these complex 

 processes and of the means by which they are controlled and 

 directed to their respective ends presents many intriguing 

 problems. Developments of the last few years have expanded 

 our knowledge of certain of these problems to an extent that a 

 basic framework begins to emerge, and it is now possible to 

 contemplate the patterns which nature has devised to achieve 

 these many specialized and remarkable functions of the blood. 



Transport Functions 



The most completely understood transport mechanism is 

 without doubt that by which oxygen is carried from the lungs to 

 the tissues. This familar process is based upon the reversible 

 reaction of hemoglobin and oxygen. Control and direction to 

 meet the tissue demand are accomplished through the mass 

 action principle which governs both the loading and unloading 

 phases of the reaction. Dissociation of oxygen is augmented in 

 the tissues by the effect of carbon dioxide on the affinity of 

 hemoglobin for oxygen. Moreover, since the rates of reaction 

 are rapid, they proceed without the aid of enzymatic mediation. 

 The simplicity and elegance of this mechanism are enhanced 

 by its quasi-reciprocal relation to the transport of carbon 

 dioxide. The latter depends upon the decreased acidity of 

 hemoglobin following dissociation of its oxygen which "makes 

 room" for additional bicarbonate and carbamino anions. 

 Favorable transfer rates are assured by the action of the red cell 

 carbonic anhydrase in catalyzing the hydration of carbon dioxide 

 and the breakdown of carbonic acid when the reaction is re- 

 versed in the lungs. The net effect of these reactions is the 



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