RESPIRATION BEYOND THE LUNGS 407 



of C0 2 rises in the plasma both H 2 C0 3 and HC1 migrate into the cor- 

 puscles, leaving less H 2 C0 3 and more Na in the plasma and tending 



TT QQ 



therefore to hold the ratio L? at its normal level so tnat PH 

 changes only to a slight degree (from P H 7.35 in arterial blood to P H 

 7.33 in venous blood). Plasma separated from corpuscles is therefore a 

 much less efficient buffer than whole blood. If the blood be first of all 

 equilibrated with varying tensions of C0 2 and the plasma then sepa- 

 rated, it will within certain limits give the same P H as blood itself. 



To go into the various experiments upon which these conclusions 

 depend would take us far beyond the limits of this volume. Excellent 

 accounts of these experiments have recently been given by D. D. Van 

 Slyke 81 and C. L. Evans. 82 In a general way it may be said that the 

 experiments consist in determining the amounts of C0 2 taken up by 

 exposing blood or plasma at varying partial pressures of C0 2 in a tonom- 

 eter as shown in Fig. 134. From the laws of solution of gases and the 

 coefficient of solubility of C0 2 in blood (page 353) it is then possible to 

 calculate by the formula given on page 49 what the P H must be at vary- 

 ing tensions of C0 2 . Haggard and Y. Henderson 83 have contributed 

 many important results by these methods. 



Alterations in C0 2 -Content of the Blood Plasma in Certain Respiratory 

 and Circulatory Diseases. There is a difference of three to eight volumes 

 per cent in the CO 2 -content of the plasma of arterial and venous blood in 

 man during complete muscular rest. After exercise, such as walking, 

 the difference becomes much greater (12 to 15 per cent). The average 

 for arterial plasma is 56 volumes per cent, the deviations from the aver- 

 age being about - 5 (R. W. Scott 75 ). 



In chronic cardiac disease (rheumatic myocarditis and valvulitis), with- 

 out vascular or renal complication, the carbonate of the plasma of both 

 arterial and venous blood (taken while the patient is at rest) is very de- 

 cidedly below the normal, the arterial C0 2 being also much more variable 

 than usual, and the discrepancy between venous and arterial bloods more 

 marked. The lowest values were found by R. W. Scott to occur in cases 

 in which dyspnea was a marked symptom, which indicates that the cause 

 for the low C0 2 value must be increased alveolar ventilation due to excite- 

 ment of the respiratory center by inadequate oxygenation of the blood 

 (anoxemia). When the condition is treated by rest in bed and the circula- 

 tion becomes restored to normal, the C0 2 -content of the arterial blood re- 

 turns towards the normal. 



In cases of chronic pulmonary emphysema without circulatory or renal 

 complications the C0 2 -content of arterial and of venous blood plasma is 

 markedly raised (values such as 80.2 for arterial plasma and 88.4 for 

 venous having been obtained). These patients show another remark- 

 able peculiarity, namely a great tolerance towards C0 2 in the inspired 



