194 RESPIRATION 



capacity of the blood for combining with COg. In other words the 

 dissociation curve of the CO2 in blood, if plotted as in Figure 25, 

 would occupy a higher position. This is evidently a change tending 

 to counteract the diminished blood alkalinity produced by the 

 excess of COg. 



The same observers found that on prolonged and forced arti- 

 ficial ventilation of the lungs, so as to produce a condition of al- 

 kalosis, there is a corresponding diminution in the capacity of the 

 blood for combining with CO2. This is also a change towards 

 the normal alkalinity. Thus in an alkalosis produced by excessive 

 \ removal of CO2 the av^ailable alkali in the blood diminished, while 

 '' in an acidosis produced by excess of CO2 the available alkali 

 increased. It is clear that in either case the change is of a character 

 tending to neutralize the change in blood reaction. 



What is the significance of this change? It occurs much too 

 quickly to be capable of explanation as due to an adaptive re- 

 sponse by the kidneys and liver. The probability is, therefore, that 

 it is due to exchange of anions between the tissues and blood in 

 the manner discussed in Chapter IV (Addendum), and is indica- 

 tive, therefore, of very severe alkalosis or acidosis of the tissues. 

 This would help to account for the very dangerous symptoms 

 which Henderson and Haggard found to be an accompaniment of 

 any considerable diminution of the available alkali of the blood, 

 when the diminution was produced by excessive artificial respira- 

 tion. Thus a diminution of about 40 per cent in the capacity of 

 the blood for combining with CO2 was fatal to the animal. A 

 similar diminution due to the acidosis caused by running quickly 

 up a stair is hardly felt at all. In the latter case the diminution in 

 available alkali in the blood indicates a quite trifling acidosis, 

 while in the former a similar change in the blood indicates a 

 severe and fatal alkalosis. 



These and other experiments*^ of these investigators brought 

 out in a striking manner that it is a complete mistake to regard 

 diminution of the available alkali (or so-called "alkaline reserve") 

 of the blood as a definite sign of acidosis in the living body. The 

 "alkaline reserve" of the blood and whole body is only another 

 name for its "titration alkalinity" ; and it has already been shown 

 above that titration alkalinity is no measure, and not even a sure 

 qualitative indication, of the real alkalinity of the blood. In the 

 experiments of Yandell Henderson and Haggard the animals were 



"Haggard and Henderson, Journ, of Biol. Chem., XXXIX, p. 163, 19 19; 

 and XLIII, pp. 3, 15, and 29, 1920. 



