HYDROGEN ION CONCENTRATION AND PROTEOLYSIS. 165 



These different constituents were sterilized separately before mixing. 

 The medium which was thus prepared maintains the figured Ph fairly 

 closely, and also the amount of formol titrating nitrogen becomes uniform, 

 as shown below. 



Table VI. — Addition of Acid and Alkali to the Medium, and their Influence 

 upon the Formol Titrating Nitrogeyi. 



1 Milligrams in 100 cubic centimeters broth. 



The results indicate that the two methods, colorimetric and electro- 

 metric, give better comparative results where Ph is greater than 6, or 

 directed toward alkalinitJ^ There is, however, a marked difference when 

 it is directed toward acidity. This may be due to the nature of the indi- 

 cators used. Again, this last experiment was carried out making the total 

 volume to 10, while the amount of n/5 HCl and n/5 NaOH was deter- 

 mined previously by adding a certain amount of the acid or alkali to 

 10 cubic centimeters. These factors undoubtedly influenced the results 

 to some extent. In the preparation of the medium used for the proposed 

 investigation, all these factors and precautions have been observed. 



Besides these, still another factor has been taken into consideration in 

 carrying out this investigation. The amount of medium added at the 

 time of inoculation may influence the results. 



