RESPIRATION 



267 



The manner in which carbon dioxide exists in the blood is more diffi- 

 cult of explanation. Besides being dissolved in the watery plasma and 

 corpuscles, it is believed that the carbon dioxide is in part loosely com- 

 bined in the blood-plasma as a weak acid, attached to the alkali present 

 and to the proteins, and also to the red corpuscles, particularly 



10 



40 



60 



60 



70 



80 



FIG. 139. EFFECT OF HAEMOGLOBIN SOLUTION AND OF SALTS ON OXYGEN 

 DISSOCIATION CURVE. (Barcroft.) 



I. Dissociation curve of haemoglobin dissolved in water. 



U. .. ,, '7% NaCl 



III. -9% KC1 



Ordinate = percentage saturation of haemoglobin; abscissa = tension of oxygen in 

 millimetres of mercury. Rectangle surrounding point = magnitude of experi- 

 mental error. Temperature 37-38 C. 



the protein portion (the globin) of the haemoglobin. Haemoglobin 

 consists of 95 per cent, globin and 5 per cent, haematin; the 

 oxygen is attached to the latter, which contains the iron. Two in- 

 teresting facts have been shown in regard to the chemical combina- 

 tion of C0 2 in the blood: first, that in spite of the presence of free 

 alkali, blood but not plasma gives up almost all its C0 2 to the 



