1190 



PHYSIOLOGY 



probable that the action on the carbonates of the plasma is due not so 

 much to the haemoglobin as to an interchange of acid radicals between 

 the corpuscles and the plasma. If carbon dioxide be passed into 

 defibrinated blood the alkalinity of the plasma increases while the 

 chlorides diminish, and it is probably the reverse interchange of 

 radicals between corpuscles and plasma which is responsible for the 

 evolution of carbon dioxide on the addition of corpuscles to plasma 

 in vacuo. 



THE ALKALINITY OF BLOOD. Blood-plasma is generally de- 

 scribed as slightly alkaline, and its alkalinity is measured in terms 

 of deci- or centinormal acid. The term alkalinity is relative. Caustic 

 alkali owes its alkalinity to the presence of OH ions. The neutrality 

 of distilled water is due to the presence of practically equal amounts of 

 H and OH ions in the fluid. We may measure the concentration of 

 H or OH ions in a fluid electrically.* If this electrical method be 

 applied to blood or blood-plasma it reveals either of these fluids 

 as practically neutral, i.e. there is little or no greater concentration of 



* By the use of different indicators we may arrive at some conclusion as to 

 the approximate concentration of hydrogen ions in any given liquid. In the 

 following Table are set out, from a paper by Roaf, the colour's of a number of 

 different indicators, and the degree of acidity which is sufficient to change their 

 colours : 



It should be remembered that in distilled water of the highest state of purity 

 the concentration of H and OH ions respectively is about 1 x 10 7 , 



