RESPIRATION 



oxygen the difference would be .07, as shown in Figure 56 from 

 Parsons's paper. Assuming, however, that the mixed venous blood 

 loses normally a fourth of its combined oxygen (see Chapter X), 

 the difference is only .0175 a difference which can hardly be 

 detected except by physiological methods, and which corresponds 

 to a rise of only 0.3 per cent in the alveolar CO 2 percentage. 



It might be supposed that in order to obtain the true PH of 

 arterial blood under abnormal conditions all that is necessary is to 

 add a constant to the value obtained for reduced blood; and that 

 consequently the ordinary methods of determining PH (whether 

 electrometrically or from indications given by the dissociation 



7-6 



7-5 



7-3 



7-2 



1-1 



40 50 60 70 



TOTAL C0 t CONTNT(c.c/ iQoc J OF BLOOD 



Figure 56. 



The slope of the line AC shows the rate at which the PH 

 of blood increases as its content of CO 2 increases in the 

 capillaries. 



curve of oxyhaemoglobin) give reliable indications of any altera- 

 tion in the PH of the arterial blood. There is, however, no evidence 

 at present that this is the case, and there is in fact other evidence 

 pointing in the opposite direction. 



If, in the first place, the proportion of haemoglobin in the blood 

 is altered, there will presumably be an alteration in the difference 

 between the PH of fully oxygenated and of reduced blood. Apart 

 altogether from this, however, there may be another kind of al- 

 teration in this difference. In the paper by Christiansen, Douglas, 

 and myself, it was pointed out that the probable reason why re- 

 duced blood appears to be more alkaline than oxygenated blood 

 is that on reduction the haemoglobin becomes more aggregated 

 and therefore acts less strongly as an acid. In abnormal blood the 

 degree of increased aggregation may be either increased or di- 

 minished. This will alter the difference in PH between oxygenated 

 and reduced blood, and will also, if our theory as to the cause of 



