THE RELATIVE EFFECT OF PHOSPHATE-ACETATE 

 AND OF PHOSPHATE-PHTHALATE BUFFER MIX- 

 TURES UPON THE GROWTH OF ENDOTHIA PARA- 

 SITICA ON MALT EXTRACT AND CORN MEAL MEDIA 



M. R. MEACHAM, J. H. HOPFIELD and S. F. ACREE 



Received for publication February 27, 1920 



As described in another report, 1 a mixture 2 of acetic acid and 

 dipotassium hydrogen phosphate (K 2 HP0 4 ) has been used in in- 

 creasing the buffer effect of several media. As the writers had 

 observed that some kinds of organisms grow upon rather weak 

 solutions of potassium acid phthalate, it was thought well to try 

 the latter salt instead of acetic acid as a buffer material and to 

 test further its effect upon the growth of E. parasitica (Murr.) 

 Anders, for which it was desired to use the buffered media. Al- 

 though acid potassium phthalate and dipotassium hydrogen phos- 

 phate do not give as straight a buffer curve as do the acetic acid 

 and dipotassium hydrogen phosphate, and hence have not been 

 used in general culture work, the following results may be of 

 value. 



The media used were 2.5 per cent malr extract agar or corn 

 meal extract agar buffered with M/50 molar K 2 HP0 4 plus either 

 M/50 acetic acid or M/50 acid potassium phthalate. The pH 

 values of these media are about 5.7 and do not vary from each 

 other in pH by more than 0.2. This pH is at or near the opti- 

 mum for the organism, as reported in another paper, 3 but is also 



1 Paper read before the Meeting of the American Chemical Society at Phila- 

 delphia, September, 1919, and appearing soon in the Journal of Bacteriology. 



2 We also make the same mixture by using weighed quantities of pure anhy- 

 drous sodium or potassium acetate and potassium dihydrogen phosphate in prop- 

 er proportions. Each salt can be sterilized separately in weighed quantities 

 and the mixture can be made afterwards under sterile conditions. 



8 See an article appearing in the Journal of Bacteriology in March, 1920. An 

 exhaustive report on the work on Endothia parasitica will appear in the near fu- 

 ture. See Science 48: 449-450, November 15, 1918. 



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