40 PHYSICOCHEMICAL BASIS OF PHYSIOLOGICAL PROCESSES 



Nevertheless, Van Slyke's definition has a real value, because it em- 

 phasizes the importance of a determination of the bicarbonate as a cri- 

 terion of the degree of the forms of acidosis usually met with in disease. 

 The bicarbonate under such conditions may become reduced either be- 

 cause of the appearance of improperly oxidized fatty acids, like /?-oxy- 

 butyric and acetoacetic, when carbohydrate metabolism is upset as in 

 diabetes or starvation, or because the acids produced by a normal 

 metabolism are inadequately eliminated by the kidneys, as in nephritis. 



Accordingly, if the respiratory mechanism and increased mass move- 

 ment of the blood (for an increase in C H accelerates this also) should 



TT f^Ci 



fail to eliminate C0 2 quickly enough so as to keep the -n-pr? ra tio at 

 one twentieth, then C H will rise. This is not likely to happen until a 

 large part of the NaHC0 3 has been used up, so that an estimation of that 

 actually present must be a reliable index of the proximity to this 

 condition. 



A sustained increase in C H is incompatible with life. The NaHC0 3 is 

 the buffer, the factor of safety which prevents its occurrence. Although 

 it is only in arterial blood (i. e., after elimination of excess of C0 2 by 



TT r^r\ 

 the lungs has been accomplished) that constancy in the ratio 2 * 



.vv'o 



can be expected, it is fortunate, for practical reasons, that venous blood 



collected during muscular rest and without stasis should be only slightly 

 different. 



When acids are added to the blood, they will first of all be neutralized 

 by the "buffers" of the plasma namely, NaHC0 3 (and protein), as we 

 have seen. But this is only the first line of defense against acidosis, for 

 buffer substances present in the corpuscles may also be used. This intra- 

 corpuscular reserve of base is supplied partly by transference of K 

 and Na from corpuscle to plasma, but mainly by that of HC1 from the 

 plasma into the corpuscle, so releasing base in the former to combine 

 with the added acid (e. g., H 2 C0 3 ), according to the equation: 

 H 2 C0 3 + NaCl * NaHC0 3 i- HC1. The HC1 on entering the corpuscle 

 reacts with phosphates according to the equation: HCl + Na 2 HP0 4 ^ 

 NaH 2 P0 4 + NaCl. This is a particularly important, detail of the buffer 

 action of the blood, not only because it shows us how the phosphates of 

 the corpuscles (of the blood of species in which much phosphoric acid is 

 present) are rendered available for neutralizing acids added to the plasma, 

 where there are practically no phosphates, but also because the transference 

 of acid must go on with the other cells of the body, so that the plasma, 

 itself rather poor in buffer substances, has all those of the body at its 

 disposal. 



