492 M. R. MEACHAM, J. H. HOPFIELD AND S. F. ACREE 



ture is clear when we recall that the most important range of 

 acidity in biological work is from a pH of 3 or 4 up to 8 or 9. 

 But it is in just this region that we find the largest change in 

 pH, and therefore the largest errors, when acid or alkali is added to 

 the usual unbuffered culture media made from corn meal, beef, 

 etc., which have small buffer properties. This is illustrated 

 clearly in figure 1, where it is shown that, in adjusting a medium, 

 an error of only 0.2 cc. of N/1 alkali in 100 cc. of corn meal extract 



14 



Figure 



Curves Showinq 

 the 



elative Buffer Effect 



A. Corn metl end Corn ff»ur ms</,* 



B. £.%/£ /lalt *xtraetm*di>"rt- 



C. fit an deeocfi°r\. 



D. CteS/hv? £>arf< extract 

 E U/«Ar 



CC.,PER 100 CC. OF 

 MEDIUM, OF ADDED 



Fig. 1 



changes the pH from about 4 to 10 and hence reduces the hydrogen 

 ion concentration from 10~ 4 (or N/10,000) to one-millionth that 

 value, or to 10~ 10 (or N/10,000,000,000). If the medium con- 

 tains a mixture of buffer acids giving a smooth titration curve in 

 this important biological range any desired acidity of the medium 



ionization constants of asparaginic, phthalic, tartaric, glycerophosphoric, citric 

 and pyrophosphoric acids. The theory is equally useful for analyzing a total 

 titration curve back into the separate titration curves for each acid (or base) 

 originally present or formed by the bacteria, or for calculating the total titration 

 curve from the separate titration curves for the individual acids (or bases). 



