372 THE RESPIRATION 



attention will be devoted in the next few pages to some of the researches 

 which have been made bearing on the relationship between the C0 2 of 

 the alveolar air and the various modified types of breathing that can be 

 produced experimentally or which become developed under altered physi- 

 ological conditions. 



As we have seen, much work concerning the physicochemical principles 

 involved in the control of the reaction of the blood has been contributed 

 during recent years by physical and biological chemists, but much of this 

 work in our judgment fails to pay sufficient regard to the extraordinarily 

 complicated conditions existing in the animal body, and more particu- 

 larly, to correlate the purely physicochemical data with the numerous 

 observations that have from time to time been recorded by physiologists 

 regarding the behavior of the respiratory center. Physical chemists have 

 recently, for example, gone so far as to define acidosis as a condition in 

 which there is a diminution in the bicarbonate content of the blood in- 

 duced by the discharge into it of fixed acids. This is going too far, for 

 it fails to recognize acidosis due to an increase in the C0 2 of the blood. 



It is the molecular ratio XT* which determines the tension of C0 2 . 



LJNa-ti.v_/O3 J 



When C0 2 is added to the blood, either experimentally by respiring the 

 gas, or naturally. owing to muscular exercise or to pathological conditions in 

 which there is a deficient excretion of C0 2 , as in heart disease, the ten- 

 dency of the equation to change, by increase of the numerator, is pre- 

 vented partly by stimulation -of the respiratory center, which gets rid of 

 C0 2 , and partly by an increase in the denominator. The respiratory 

 center is so sensitive to slight increases in C H that it becomes excited 



before a sufficient increase in H 2 C0 3 has occurred to disturb the normal 



rTT r<f\ -i 

 w ^rnA When fixed acids are added to the blood the denom- 



L iNa-biGUs. J 



inator of the equation, NaHC0 3 , is lowered and consequently C H rises, 

 and increased respiration occurs, lowering H 2 C0 3 and thus reestablishing 

 the ratio. 



