374 THE RESPIRATION 



in last column; B' = figures in first column; A = aqueous tension of alveolar air;_ P' = figures of 

 second column; B barometric pressure at sea level. A is obtained from tables giving the aqueous 

 tension at different temperatures. 



The Alveolar C0 2 -Tension in Conditions of Anoxemia 



The foregoing observations have shown that the respiratory hormone 

 is related to the tension of C0 2 in the blood supplying the respiratory 

 center, and that this tension acts partly by causing alteration in C H 

 of the blood, and partly because C0 2 has direct effect on the center. These 

 conclusions do not imply that other changes in the composition of the 

 blood may not act on the respiratory center, indeed there is plenty of 

 evidence to show that deficiency of oxygrw fffl fhe ^^-^ 1 blood or anoxe- 

 mia also acts. This influenceTs, howeverTless evidentjliaji .that of changes 

 in^^HjDr^XlJD^-and it varies with the degree of deficiency, being stimulatory 

 when the deficiency is moderate, and inhibitory when it is extreme. It is 

 not surprising, therefore, that some considerable confusion should have 

 existed as to the precise role of 2 deficiency in its effect on the respira- 

 tions and it is only within the last year or two that the problem has been 

 satisfactorily elucidated. 



The most important indication that alterations in the C0 2 -tension of the 

 blood cannot alone be responsible for changes in respiratory activity is 

 afforded by the observation that the alveolar C0 2 does not always, as in 

 the cases described in the previous chapter, run parallel with alveolar ven- 

 tilation. The opposite relationship often obtains, namely, decreased al- 

 veolar C0 2 and hyperpnea (see page 379), and it is our purpose in the 

 present chapter to show how this is often associated with a condition of 

 oxygen deficiency. It is most important that we consider this phase of the 

 subject in some detail because of the application which it has in the eluci- 

 dation of many problems of respiratory disturbance, as met with in the 

 clinic. The disturbances in respiratory function which can be brought 

 about experimentally in normal animals are in many cases exactly like those 

 which are met with in various diseases, particularly those which depend 

 on inadequate absorption of oxygen by the blood. 



The General Effects of Deficiency of Oxygen, or Anoxemia. Various 



