RESPIRATION AND ACIDOSIS 



315 



it. The levelling bulb is then raised hi the left hand while with the right the 

 cock is turned so as to connect the pipette with c. The mercury flowing in from 

 c fills the body of the pipette, and as much of the calibrated stem at the top as 

 is not occupied by the gas extracted from the solution. A few hundredths of 

 a c.c. of water which could not be completely drained into d float on top of the 

 mercury in the pipette, but the error caused by reabsorption of carbon dioxide 

 into this small volume of water is negligible if the reading is made at once. The 

 mercury bulb is placed at such a level that the gas in the pipette is under atmos- 

 pheric pressure 1 and the volume of the gas is read on the scale. 



Calculation. By means of the table on page 316 the readings on the apparatus 

 can be directly transposed into c.c. of carbon dioxide chemically bound by 100 

 c.c. of plasma. The barometer reading and room temperature are taken at 

 the time of the determination. For convenience hi the calculation values are 



B 

 given below for the ratio ->- over the range usually encountered. 



In case the volume of plasma taken for estimation of carbon dioxide content 

 was 0.5 c.c. the observed volume of gas is multiplied by 2 before it is used to 

 calculate the volume per cent of carbon dioxide bound. 



Interpretation. The carbon dioxide capacity of the plasma as 

 determined by this method appears to indicate not only the alkaline 

 reserve of the blood but also that of the entire body. The average 

 normal value for man is 65 volume per cent of carbon dioxide. The 

 table, page 317, shows the range of results obtained with normal and 

 pathological plasma, as well as the relationship of the plasma bi- 

 carbonate to acid excretion, alkali tolerance, and alveolar carbon 

 dioxide tension. 



1 In order to have the column in the pipette exactly balanced by that outside, the surface 

 of the mercury in the levelling bulb should be raised until it is level with the mercury 

 meniscus in the pipette, and then, for entire accuracy, raised above the latter meniscus 

 by a distance equal to Y\ the height of the column of water above the mercury in the 

 pipette. As the water column is as a rule, only about 10 mm. high, the correction that 

 has to be estimated is less than i mm. of mercury, i. e., the entire correction for the water 

 column is not enough to influence results appreciably. 



