78 DONALD D. VAN SLYKE 



would accurately locate the point on a diagram like that of Figure II, and 

 would indicate the nature of the blood condition. 



Of the three values, the two which are most simply and accurately de- 

 termined by the technique available are the bicarbonate concentration and 

 the pH. The third value, the H 2 CO 3 , requires at present for its estimation 

 a plotting of the CO 2 absorption curve of the blood examined, and for re- 

 liable results the determinations involved, which include a correction for 

 the oxygen unsaturation of the hemoglobin, make unusual demands on both 

 time and skill. CO 2 absorption curves of clinical cases have nevertheless 

 yielded results of decided interest in the hands of Peters and Barr (1921) 

 and of Means, Bock, and Woodwell (1921), and the reader is referred 

 to Peters and Barr for the technique. In their work, absorption curves 

 were desirable to throw light on questions of respiratory pathology, in 

 particular on CO 2 tension equilibria between blood and alveolar air, as 

 well as on the acid-base balance. 



For determination of the acid-base balance, however, we can simplify 

 both the technique and the diagram for interpreting results by leaving 

 out the H 2 CO 3 and devoting our attention to the BHCO 3 and the pH. If 

 we plot curves showing the possible blood conditions, with the BHCO 3 

 values as ordinates, the pH or H + values as abscissae, we obtain Figure 

 3 for whole blood and Figure 4 for plasma. 



For the complete technique of the pH and BHCO 3 determinations the 

 reader is advised to consult the original papers cited below. We shall, 

 however, outline the principles on which the methods are based, and the 

 more especial precautions required when they are applied to the blood. 



Collection and Treatment of Blood Samples. In collecting and han- 

 dling blood, the following precautions are of importance : 



(1) For at least one hour before the blood is drawn the subject should 

 avoid vigorous muscular exertion, as this, presumably because of the lactic 

 acid formed, lowers the bicarbonate of the blood (Christiansen, Douglas, 

 and Haldane, 1914; Morowitz and Walker, 1914). It also appreciably 

 lowers the pH (Parson, Parsons, and Barcroft, 1920). 



(2) If venous blood is used undue accumulation of CO 2 is avoided 

 by avoidance of stasis, and by keeping warm the arm from which the 

 blood is drawn. 



(3) Within an hour or two after human blood is drawn the cells begin 

 to form acid products (Christiansen, Douglas, and Haldane, 1914) with 

 a resultant fall in both pH and bicarbonate. Consequently one must either 

 analyze the whole blood within an hour after it leaves the body, or centrif- 

 ugate it within that time and perform the analyses on the plasma. 



(4) No opportunity must be given for escape of CO 2 , either when the 

 blood is drawn or during its subsequent handling, or the pH will rise 

 and the bicarbonate will fall. Exposure to air must be entirely avoided. 

 A layer of paraffin oil over blood in a tube standing quietly prevents ap- 



