THE DETERMINATION OF pH AND CARBON DIOXIDE ON A SINGLE SMALL SAMPLE OF BLOOD PLASMA OR SERUM

Economy of blood is always desirable provided the determination gives the required accuracy. Children’s veins are difficult to puncture; in infants the longitudinal sinus must be used to obtain a reasonable quantity of blood without stasis. Small quantities, 1 to 2 cc., can be obtained from the heel by Drucker and Cullen’s method (1). In small animals, such as the rat, it is necessary to utilize methods that economize material or else use the pooled blood of several animals. At present there are no reports on the acid-base equilibrium of single rats. Van Slyke’s method (2, 3) for COz determinations leaves little to be desired for elegance and accuracy; Hastings and Sendroy’s method (4), though recently shown to involve variations from the electrometric method which are at present not understood, has probably never led to any false clinical interpretation. Eventually these variations will be understood and corrected, for the method is simple and free from errors of manipulation. Moreover, the electrometric method may be subject to large errors when made by the refill technique, and as usually carried out requires several cc. of material. To combine these two methods on a single sample of material, it is necessary only to measure the pH calorimetrically in 0.9 per cent saline and then, without exposure to air, to transfer the material to the Van Slyke gas apparatus.