1 82 RESPIRATION 



this inference was shortly afterwards established by Ryffel, 18 who 

 had meanwhile worked out a new and very convenient method of 

 determining small amounts of lactic acid in blood and urine. 



The methods of determining hydrogen ion concentration in the 

 blood were at that time still too crude to permit of testing these in- 

 ferences by direct determinations, but shortly afterwards the elec- 

 trometric method was greatly improved by Sorensen and particu- 

 larly by Hasselbalch of Copenhagen. In 1912 Hasselbalch and 

 Lundsgaard 19 published curves showing the variations of hydro- 

 gen ion concentration with variations in CO 2 pressure at body 

 temperature in ox blood, and Lundsgaard 20 repeated the experi- 

 ments with human blood. Figure 54 shows graphically their re- 

 sults for blood and other liquids. For convenience' sake the results 

 for hydrogen ion concentration are plotted, not directly in terms of 

 gram molecules per liter, but in terms of the negative power of TO 

 representing this value. This mode of notation, introduced by 

 Sorensen, is represented by the symbol PH, and since the negative 

 power increases with diminution of hydrogen ion, or increase of 

 hydroxyl ion concentration, the curve rises with diminution of 

 hydrogen ion concentration. 



At body temperature the point of neutrality corresponds to a 

 PH about 6.78, as indicated by the thick line in the figure. It will 

 be seen from the curves that even with a far higher pressure of 

 CO 2 than exists in the living body the neutral point is not 

 reached. This is partly due to the fact that the proportional ioniza- 

 tion of carbonic acid becomes less and less with increasing con- 

 centration, just as is the case with other acids, including even 

 strong ones. The lower curve (for neutral potassium chloride solu- 

 tion) shows this clearly. Thus sulphuric acid when pure is quite 

 devoid of acid properties and does not attack metals, because it is 

 practically not ionized at all. This can be understood on the 

 theory, already alluded to, that ionization in aqueous solutions is 

 brought about through a reversible reaction with the water mole- 

 cules. 



The influence of a buffer substance (disodium phosphate) in 

 hindering changes of hydrogen ion concentration is shown very 

 strikingly in the two curves for phosphate solutions. In blood, as 

 already pointed out, various buffer substances, including haemo- 

 globin with other proteins, and the phosphate in the corpuscles, 

 are present. The curve for acidified blood shows that even when 



18 Ryffel, Journ. of Physiol., XXXIX, Proc. Physwl. Soc., p. xxix, 1910. 



19 Hasselbalch and Lundsgaard, Bwchem. Zeitschr., XXXVIII, p. 77, 1912. 



20 Lundsgaard, Btochem. Zeitschr., XLI, p. 247, 1912. 



