298 Appendix I. On methods 



Measurement of C. 



Take the apparatus out of the bath, open the taps. Take the bottle L. Put 

 potassium ferricyanide into the reservoir, replace the bottle, put the apparatus in the 

 bath, and proceed as in the determination of the oxygen capacity. 



Let the measurement of C give a pressure of 60 mm. 



The percentage saturation = 100 i.e. 68 / . 



This determination gains considerably in accuracy owing to the fact that neither 

 the quantity of blood used nor the constant of the apparatus enters into the calcula- 

 tion. There is therefore no need to calibrate the pipette used or even to exercise 

 extreme caution in measuring the amount of blood used for the experiment. 



It is of course unnecessary to correct for temperature and pressure, the correction 

 affecting B and C alike. On the other hand one must reckon with the fact that the 

 unsaturated blood will take up nitrogen and oxygen from the air of the apparatus in 

 which the blood is shaken in quantities which depend upon the composition and 

 temperature of the gas with which the blood has previously been in equilibrium. 



The general principles upon which the calculation for this correction is made are 

 set out under the measurement of oxygen in unsaturated blood. For blood taken 

 from a tonometer at 13 % or fr m tne body it is generally sufficiently accurate to add 

 4 / to the observed saturation. 



Determination of the difference between the quantities of oxygen 

 contained in 1 c.c. of arterial and 1 c.c. of venous blood tcith 

 the differential manometer. 



If, as is usually the case, the arterial blood is nearly saturated with oxygen, 

 relatively to the venous blood, this determination is one of the easiest in blood gas 

 analysis. 



Place 2 c.c. of ammonia in each of the bottles, in L place 1 c.c. of venous blood, in 

 R 1 c.c. of arterial blood. 



See that the stoppers are greased and that they are free from all traces of ferri- 

 cyanide and that the taps are open. 



Place the bottles on the apparatus, and the apparatus with its bottles in the 

 water bath. 



After five minutes read. Suppose the readings to be 



Left Eight Zero error 



120 119-5 0-5 



Close the taps ; see that the meniscus does not move for two minutes. 

 Shake for one minute and place in the bath for one minute alternately till a 

 constant reading is obtained. Let this be 



Left Eight Diff. Zero error p 



127 112-5 14-5 -5 14 



If k be the constant of the apparatus, p x k is the difference between the oxygen 

 in the arterial and venous blood. 



A few words may be said about the limitations of this method. 



