64 DONALD D. VAN SLYKE 



The maximum available alkali of the blood is therefore the alkali 

 of the bicarbonate plus that portion of the other buffer alkali which is 

 yielded when the pH changes from normal to the minimum compatible 

 with life. The amount of such buffer alkali may be estimated by increas- 

 ing the CO 2 , tension of the blood until the pH is reduced to 6.95. All the 

 alkali given up by the other buffers is bound by the H 2 CO 3 and thereby 

 turned into bicarbonate under these conditions, so that the increase in 

 bicarbonate above that at normal CO 2 tension represents the available 

 alkali of the other buffers. By extrapolation in Fig. 3 of the average nor- 

 mal CO 2 absorption curve of human blood computed by Peter and Barr 

 (a) (1921) we find that this available alkali from buffers other than bicar- 

 bonate is about 0.01 M in concentration, or approximately half the normal 

 bicarbonate alkali. 



The average total available alkali of normal human blood may there- 

 fore be summarized as 



0.022 M bicarbonate alkali, equivalent to 49 volume per cent of 



bicarbonate CO 2 , of which % to % may be used for 

 neutralization of acid without change in pH. 

 0.010 M alkali from other buffers, available only when the pH 



falls to 6.95. 



Total 0.032 M alkali available with maximum fall in pH com- 

 patible with life. 

 Of the 0.010 M alkali from buffers other than bicarbonate the greater 



part is normally bound by hemoglobin (Van Slyke, 1921, p. 160). 



In a broad sense, therefore, the alkali reserve of the blood includes 

 not only the bicarbonate, but in addition about half as much more alkali 

 of the other blood buffers. In a still broader sense one might add the 

 tissue alkali considered below, since during acid invasion it becomes 

 available to assist in maintaining the blood neutrality. 



In the interest of clearness and convenience, however, we shall use 

 the term alkali reserve to indicate the blood bicarbonate measured at such 

 C0 2 tension that the pH is physiologically normal. This usage seems 

 desirable for the reasons that the bicarbonate as defined is a quantitatively 

 measurable value, and that it represents the only alkali in the blood that 

 can be used to neutralize acid without change in pH. Furthermore "blood 

 bicarbonate" and "alkali reserve" have for some time been used synony- 

 mously in the literature, and the above definition does not change, but 

 merely defines more accurately, the recognized conception of the alkali 

 reserve. 



2. The Respiratory Regulation of the Free H 2 C0 3 of the Blood. 

 Almost as rapid as the neutralization by the buffers is the compensation 



