ACIDOSIS 39 



by Van Slyke and others to constitute the real definition of acidosis 

 namely, "a condition in which the concentration of bicarbonate in the 

 blood is reduced below the normal level. " If the respiratory center 

 for any reason should not respond promptly enough to an increase in 



TT QQ 



the molecular ratio TTTT > an( i C H consequently become greater, the 



condition is called uncompensated acidosis, but if the center does respond 

 so that C H is held constant (although NaHC0 3 is decreased), the condition 

 is one of compensated acidosis. 



For practical reasons, therefore, the study of pathological acidosis de- 

 pends on an estimation of the bicarbonate content of the blood or, since 

 it is simpler to carry out and is of equal value, of the plasma. When 

 plasma is obtained by removing blood from a vein of the arm and cen- 

 trifuged immediately out of contact with air (so that C0 2 may not be 

 lost from it) it contains approximately 60 vols. per cent of C0 2 . Since 

 we know that the partial pressure of C0 2 in blood is equal to 42 mm. Hg 

 (ascertained from determinations of the alveolar C0 2 ) (see page 361), 

 we can calculate how much of the 60 vols. per cent must be in simple 

 solution by application of the law of solution of gas in a liquid (page 

 353'). One cubic centimeter of plasma at body temperature and at 

 760 mm. Hg (atmospheric pressure) dissolves 0.54 c.c. C0 2 , so that at 



42 



42 mm. it will dissolve 7^7- x 100 x 0.54 = 3 vols. per cent. Transcribing 



ToU 



[H 2 C0 3 ] 3 1 



the figures to our equation we get 



[NaHC0 3 ] 60 20 



This definition of acidosis leaves out of regard all conditions that may 

 TT pr\ 



raise the ratio -^ rr f by the addition of H 2 C0 3 without decomposing 

 JNaJtLvjUs 



any of the NaHC0 3 , such, for example, as occurs when an excess of free 

 carbonic acid is present in the blood plasma. Since increases in free 

 C0 2 are not infrequent in both health and disease e. g., asphyxial con- 

 ditions the above definition is not sufficiently comprehensive. When 

 we come to study the control of the respiratory center, we shall see that 



FT PO 



an increase in the ratio -A-^rf ^ sufficient magnitude to cause an 



actual increase in C H can be brought about by causing an animal to respire 

 air containing an excess of C0 2 a true acidosis, but one for which no 

 place is found in the above definition. 



*This agrees sufficiently with the result as calculated from the known values of the equation 

 2 Thus, if we take CH as 0.35 x 1Q- 7 , X as 0.605 for blood conditions, and 



K. 



s 4.4X10- 

 49.) 



K as 4.4X10- (Michaelis and Rona), we get ' = 0.605 x 0.35 x 10-' = 1 (gee a]go p 



4.4 X 10 ' 21 



