332 



PRESERVATION OF NEUTRALITY 



acts as a trigger, setting off a series of reactions resulting, finally, 

 in the restoration of neutrality. Acid is set free, say in muscle, 

 and before it can be rebuilt into the muscle complex, oxidation 

 of glucose has to take place. The introduction of this acid in a 

 minute amount has three profound effects. Firstly, it increases 

 the dissociation of oxyhaemoglobin (p. 253) setting free the needed 

 quota of oxygen, secondly, by stimulating the respiratory centre 

 (Chap. XXVI.), it speeds up the intake of o-xygen, and lastly, the 

 blood flow is increased, both locally by vasodilatation, and generally 

 by increased cardiac action. 



In the work of preserving the neutrality of the organism, the 

 blood is aided by the eliminating organs, the lungs and the 

 kidneys. 



Factors tending to preserve neutrality. 



I. In the plasma we have (a) colloids, and (b) crystalloids. 



(a) The colloids of blood plasma are mainly serum albumin and 

 serum globulin and they are amphoteric in character, i.e. they may 

 act either as acids or as bases. Experiments carried out in the 

 laboratory show definitely that, although the proteins of the 

 plasma readily combine with mineral acids, they are unable to 

 react with the weakly dissociated acids found in the body. Both 

 albumin and globulin form hydrochlorides for instance, but 

 protein lactates or carbonates are unknown. Apart from the 

 amount of CO 2 adsorbed by the colloidal particles, the blood 

 colloids can play but a small part in reducing the carbonic acid, 

 etc., produced in the organism. 



(b) Of the crystalloids in solution in the plasma, sodium 

 bicarbonate has a marked " buffer " effect. In this salt a strong 

 base is united with a weak acid and, therefore, any acid stronger 

 than H 2 CO 3 will take the place of the HCO 3 ion in its combination 

 with Na. 



For instance, 



= Sodium bicarbonate. 

 = Acetic acid. 



CH 3 COONa H 2 CO 3 



(Sodium acetate) (Carbonic acid). 



This reaction appears just to postpone matters because carbonic 

 acid is set free and, although this acid is only slightly dissociated, 

 yet, as an acid, it must be reckoned with. But the equation 



