The Hydrogen Ion Concentration of the Blood in certain Pathological Conditions, as Determined by the Hydrogen Electrode and the Indirect Methods of Barcroft and Hasselbalch.

HASSELBALCH [1913] was the first to establish the conditions under which the hydrogen electrode can be used to measure accurately the reaction of the body fluids, and he constructed curves for the PH of blood under varying C02 tensions. More recently Peters [1914] has improved Hasselbalch's method by using completely reduced blood for the'determinations, and'Parsons [1917] has shown that by the CH of blood is meant the CH of the plasma it contains, i.e. the plasma obtained by centrifuging the blood without loss of CO2-which' may be called the "true plasma" [Joffe and Poulton, 1920]. When once.the hydrogen electrode apparatus has been set up the determinations do not occupy any great length of time; but as ordinarily arranged the apparatus itself tends to be somewhat complicated. A much simplified arrangement is, however, being designed byone of us (T. R. P.) especially for use with body fluids: it is soon to be placed on the market by the Cambridge and Paul Scientific Instrument Company. In this the manipulations are reduced to a minimum. Barcroft's method [Barcroft and Peters, 1914] was introduced beforethe hydrogen electrode method had been finally perfected. It consists in determining at any required CO2 pressure the percentage saturation with oxygen of the haemoglobin of the blood at a given oxygen pressure, and from this calculating the value of log K in Hill's equation. Barcroft and Peters [1914] showed for Barcroft's blood that log K was a linear function of yp, and Hasselbalch [1916] found that in the case of six normal people the same relationship exiisted between the two values. Barcroft's method was used by Lewis, Ryflel, Wolf, Cotton and Barcroft [1913] in cases of. cardio-renal disease, by Poulton and Ryffel [1913] in cases of uraemia, and by Poulton