ACIDOSIS 49 



accompanying certain forms of renal disease (chronic interstitial nephri- 

 tis), which raises the question as to whether the retention may not be 

 due to faulty elimination of the bicarbonate rather than to its retention, in 

 order that a deficient alkaline reserve maybe corrected. It has not been a 

 very simple matter to disprove entirely this possible explanation, and ex- 

 periments of a variety of types have had to be devised in connection with 

 the problem. One of them consists in determining the effect of a second 

 dose of bicarbonate administered to an acidosis patient to whom a suffi- 

 cient amount had previously been given to render the urine just alkaline. 

 It has been found that a few grams now suffice, indicating, apparently, 

 that the alkaline reserve must have been restored to its normal level. 

 Even to this experiment the objection can be raised, however, that the 

 large doses were retained because the threshold of the kidney for the ex- 

 cretion of bicarbonate was a Very high one, and that the second, smaller 

 administration just sufficed to overstep this threshold. 



Sellards' careful work with this method seems quite clearly to establish 

 its value, however, and for practical purposes it is probably the most prac- 

 ticable test -of acidosis at present available in routine clinical work. It 

 has the important* advantage, furthermore, of being simple and of requir- 

 ing no elaborate apparatus. 



It may be advantageous in this place to classify the possible causes 

 which might lead to a want of stability in th'e C H of the blood ; that is, 

 to threatened acidosis or alkalosis, not of acidosis in the narrow sense im- 

 pliecl in Van Slyke's definition, but in the broader sense of any disturb- 

 ance in the acid-base equilibrium. 



Relationship Between OCX-content of Blood and Hydrogen-ion 



Concentration 



From the equation given on page 39, it is evident that P H can be cal- 

 culated for each partial pressure of C0 2 at which blood is equilibrated, 

 provided we know the total C0 2 -combining power and the H 2 C0 3 . We 

 have seen how the former may be determined (page 42). The free H 2 CO :J 

 is determined by multiplying the mm. of C0 2 pressure by the factor 0.0672 



which is derived from the equation _-. x - in which 0.511 is the 



7bU 1 



coefficient of solubility of C0 2 in blood at 3'8 C. (cf. gas laws, page 354). 

 If blood be exposed to various C0 2 tensions which are placed on the 

 abscissa of a chart, as in Fig. 128, page 363, and the total C0 2 with which 

 it combines at each tension be placed on the ordinates, a curve (C0 2 -dis- 

 sociation curve) is obtained and a slanting line may also be drawn on 

 the chart to show the C0 2 in simple solution (i.e., as H 2 C0 3 ). Now C H 

 at each C0 2 tension will be proportional to the ratio between the dis- 



