ACIDOSIS 77 



acidosis. If the particular function studied itself is affected, as is respira- 

 tion in narcosis or renal secretion in nephritis, it may utterly fail to indi- 

 cate an acidosis that is present. On the other hand, it is at least theoreti- 

 cally possible for it to indicate an acidosis that is absent, if the function is 

 stimulated by some other factor. The alveolar CO 2 tension, for example, 

 may be lowered by respiratory stimuli other than the blood hydrion con- 

 centration. It is known to be lowered by diminution of the oxygen ten- 

 sion of the air, also by voluntary deep breathing and by deep breathing 

 caused by psychic disturbance. 



The direct methods are those by which the acid-base balance of the 

 body itself, or of the blood as representative of the body, is studied. They 

 include the determination of the BHCO 3 and pH in the blood, and the 

 alkali retention test as performed by Palmer, Salvesen, and Jackson. The 

 results of observations by such methods are not likely to be falsified by 

 functional stimuli or inhibitions, and they furthermore may be made 

 to indicate the amount by which the body's buffer alkali content is changed. 

 The direct methods appear therefore less subject to error and more subject 

 to quantitative interpretation than the functional, and we shall consider 

 them first and in more detail. 



1. Estimation of the Blood Bicarbonate and pH. For the most com- 

 plete information which we are able to interpret concerning the state of 

 the acid-base balance of the blood, it is sufficient to determine quantitatively 

 any two of the three variables pH, BHCO 3 , and H 2 CO 3 (or CO 2 ten- 

 sion). For if two are fixed, they determine the other, which may be cal- 



TT pQ 



culated from them by the equation IP = K t X -p^mr! ? r pH = pK t -f- 



BHCO 3 . 

 log TT _.- 

 3 H 2 CO 3 



In the form of acidosis of most frequent clinical occurrence, com- 

 pensated alkali deficit, such as is usually found in diabetes, nephritis, 

 and the acidoses of children, the pH remains normal, the bicarbonate alone 

 is altered, and its change affords complete evidence for diagnosis. For 

 this reason the technique for plasma bicarbonate determination introduced 

 by Van Slyke and Cullcn (1917) has proven fairly adequate for the 

 study of the acid-base balance in these conditions. 



The preceding resume of the possible states of the acid-base balance 

 of the blood, however, shows that conditions are now known, some of which 

 may be encountered clinically, in which the pH is not normal, and which, 

 therefore, the bicarbonate alone does not suffice to show. It would be 

 impossible, for example, to tell whether a high blood bicarbonate indicated 

 the condition signified in Figure II by Area 1, Area 4, Area 7, or the 

 upper portion of Area 8, unless other data were available. A knowledge 

 of either the pH, or the H 2 CO 3 , however, in addition to the bicarbonate 



