RESPIRATION BEYOND THE LUNGS 407 



that serum absorbs practically the same amount of C0 2 as a solution 

 of bicarbonate of the same concentration, and also that the addition of 

 egg albumin or of dialysed serum to a bicarbonate solution does not 

 change its reaction towards neutral red, which it should certainly do if 

 the protein absorbed any of the C0 2 . With regard to the C0 2 carried in the 

 corpuscles, there is no doubt that the greater bulk is united with hemo- 

 globin, the remainder being combined with alkali and in simple solution. 

 The behavior of the dissociation curves both of 2 and C0 2 in blood afford 

 weighty evidence for this conclusion and it is further supported by the fact 

 that a watery solution of pure hemoglobin absorbs much more C0 2 than 

 water alone when exposed to atmospheres containing the same partial 

 pressures of C0 2 . 



Alterations in C0,-Content of the Blood in Certain Respiratory and 

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

 per cent in the C0 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 OCX-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 

 air: thus, in one case, inspiration of air containing 11.4 per cent C0 2 only 

 served to increase the minute volume of air breathed from 10 to 14 liters, 

 with mild symptoms of dizziness and nausea (R. W. Scott). In a normal 

 person a much lower percentage of C0 2 would increase the pulmonary 

 ventilation several times over the normal and the symptoms would soon 

 become intolerable. The most probable explanation for the existence 



