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A TEXTBOOK OF PHYSIOLOGY 



vacuum pump; and, secondly, that blood added to a soda solution 

 sets free C0 2 from it. The probable explanation is that the blood- 

 proteins, especially the haemoglobin and the serum globulin, by virtue 

 of their amphoteric reaction, can act as both acids and alkalies. The 

 building-stones of proteins, the amino-acids, contain both NHg and 

 COOH groups. When the partial pressure of C0 2 is low, as in the 

 lungs, these proteins act as weak acids, and turn out C0 2 . On the other 



90 



1CO 



20 



30 40 50 60 



FIG. 140. (Barcroft.) 



70 



80 



100 



Dissociation curves I., II., III., IV., and V. correspond to 16, 25, 32, 38, and 49 k C. 

 respectively. Oxygen pressure plotted horizontally, percentage of reduced 

 haemoglobin vertically downwards 



hand, when the CO, pressure is high, as in the tissues, it seems 

 probable that these proteins act as alkalies, and actually combine with 

 the C0 2 and aid in its transport away from the tissues. 



That the corpuscles help to expel the C0 2 is shown by the fact 

 that acid must be added to plasma in order to obtain all the C0 2 

 combined with it. exposure to a vacuum not being sufficient by itself 

 wholly to decompose the C0 2 compounds in the plasma. 



