430 THE PRESERVATION OF NEUTRALITY 



effect produced, on the internal and external structure of bone, of 

 altering the incidence of a load. Not only are the nearby bones 

 altered, but even distant and apparently unaffected bones undergo 

 changes. In our study of the transport system we saw how an 

 alteration produced in one part of an organism spread throughout 

 the whole animal. 



One of the main functions of blood is to maintain constant the 

 concentration of hydrogen ions throughout the organism. A 

 slight potential increase in the acidity or alkalinity of the system 

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

 in the restoration of the status quo. 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 oxyhsemoglobin (p. 328) setting free the needed 

 quota of oxygen, secondly, by stimulating the respiratory centre 

 (Chap. XXVI.), it speeds up the intake of oxygen, and lastly, the 

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

 by increased cardiac action. 



In the Avork 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 and carbonates are unknown. At the hydrogen ion 

 concentration of blood, however, the proteins may act as weak 

 acids and combine with some of the plasma base. When carbon- 

 dioxide passes into the plasma it reacts with the protein salt, 

 liberating the protein as a weak acid, and forming sodium bicarbo- 

 nate with the base. The weak protein acid is so slightly dissociated 

 as to have a negligible influence on the hydrogen ion concentration. 



Some carbon-dioxide may also be absorbed by the colloidal 

 particles, but the part played by the serum proteins in the preserva- 

 tion of neutrality is quite small. 



(6) As has been stated, the main crystalloids of the plasma are 

 sodium bicarbonate and sodium chloride, but there are small 



