Y. Henderson and H. W. Haggard O00 
level of CO. and alkali back toward the normal level is resisted 
by the action of the respiratory center or allowed to develop 
only gradually. 
In this paper we shall give the experiments in which a high 
level of CO, and alkali, or hypercapnia, was induced. In suc- - 
ceeding papers experiments producing low levels of COs, or 
acapnia, will be presented. 
Theoretical. 
Attention at present is fixed so exclusively upon C, that we 
must specifically point out that actually this “physiological con- 
stant’’ only varies imperceptibly. Even these slight variations 
induce powerful counteracting efforts. Through these efforts 
nearly normal equilibrium in respect to C, is attained at highly 
abnormal levels of CO.: alkali. Thus, as we see it, interest should 
now shift, at least for the physiologist, from C, and the physico- 
chemical equilibrium to these levels of COz:alkali and the physio- 
logical equilibrium. 
The physicochemical equilibrium (L. J. Henderson) is oy 
proximately the balance of CO, against NaHCO; to maintain H, 
that is, C,, in the expression: 
Pulmonary Blood. 
air. 
+ ae 
CO, =/DissolvedCO,— H2CO3;— H sh HCO3 
he 
NaHCO; = Na + HCO; 
On the other hand the physiological equilibrium and the re- 
spiratory activity by which any great and sudden changes in Cy 
are prevented may be expressed, for example, at three levels of 
CO, and alkali as shown in the following table. 
The numerator (H:CO3) is always proportional to the alveolar 
CO, because the amount of CO, dissolved (not combined with 
alkali) is determined by the tension of CO: in the alveolar air 
(law of Henry). The alveolar CO, is of course always inversely 
proportional to the pulmonary ned Melon per unit mass of CO: 
eliminated. 
