THE INTEGRATIVE ACTION OF THE VASCULAR SYSTEM 24 1 



reaction of the blood is determined by the relation of H2CO3 

 to NaHCOs existing in the blood. If the carbonic acid is 

 increased the blood is more acid; if the carbonic acid is 

 decreased, as it may be by excessive voluntary ventilation of 

 the lungs and consequent removal of carbon dioxide from 

 the blood, the blood is more alkahne. If a non-volatile 

 acid, such as hydrochloric acid (HCl) is added to the blood, 

 it unites with the sodium of some of the sodium bicarbonate 

 and drives off carbon dioxide, according to the following 

 equation: 



HCI + NaHCOs = NaCI + H^O + CO2 



The NaCl is common salt, a neutral harmless substance. 

 The H2O and CO2 form the famihar carbonic acid, which 

 is volatile. The addition of the strong acid (HCI) has, to be 

 sure, made the blood more acid by increasing the H2CO3, 

 but, as we have seen, this stimulates the respiratory mechan- 

 ism and thus the extra carbon dioxide is quickly and readily 

 reduced. And when it is reduced the normal ratio of H2CO3 

 to NaHCOs returns, the neutrahty of the blood is restored, 

 and the deeper breathing stops. 



The sodium bicarbonate has served to protect the blood 

 from becoming acid in the circumstances just described, 

 and because of its capacity to perform that function it is 

 called a "buffer" salt. Another buffer salt existing in the 

 blood, especially in the red blood corpuscles, is alkaline 

 sodium phosphate (Na2HP04). When acid is added to blood, 

 not only is it "buffered" by sodium bicarbonate but also 

 by the alkaline sodium phosphate, according to the following 

 equation: 



Na2HP04 + HCI = NaH2P04 + NaCl 



Again note that common salt (NaCl) is formed and acid 

 sodium phosphate. It happens that both "alkaline" and 

 "acid" sodium phosphate are almost neutral substances. 

 The strong hydrochloric acid (HCI) has, therefore, not 

 altered the reaction of the blood to an important degree by 

 changing the alkahne to the acid form of the sodium phos- 

 phate. The acid phosphate has, however, a slightly acid 

 reaction and it must not be permitted to accumulate in the 



