420 K. G. DERNBY AND J. BLANC 



the microorganisms, and especially as to the ''limiting pH value" 

 we are very doubtful whether it bears any deciding significance. 

 The essential thing is to determine the optimum, and, even if this 

 should change a little under different conditions, to fix such an 

 initial reaction of the medium as can easily be reproduced and 

 allow a sufficient growth. 



In the first part of this paper we have determined the rela- 

 tion between growth and hydrogen ion concentration for a cer- 

 tain number of anaerobes, and in the second part we have studied 

 the proteolytic activity of filtrates from Clostridium sporogenes 

 and Clostridium histolyticum. 



I. THE OPTIMAL HYDROGEN ION CONCENTRATION FOR THE 

 GROWTH OF SOME ANAEROBES 



The following microorganisms have been studied: 

 Clostridium sporogenes A (Klein-Metchnikoff) 

 Clostridium sporogenes 0, isolated from horse excrements 

 Clostridium canadiense, isolated by Blanc from a case of gangrene 

 Clostridium histolyticum (Weinberg-Seguin) 

 Clostridium putrificum (Bienstock) 

 Clostridium perfringens (Veillon-Zuber) 



For all these microorganisms the same broth medium was used. 

 This was made up in the following way: 1 kgm. finely chopped 

 veal was immersed in 2 liters of tapwater and allowed to 

 autolyze at 37° for twenty-four hours; thereafter boiled and 

 filtered; 0.5 per cent NaCl and 1 per cent pepton added; then 

 steriUzed at 110° for twenty minutes. In preparing an experi- 

 ment the same amount of broth was divided among nine flasks 

 to which different amounts of HCl or NaOH were added, in order 

 to obtain certain hydrogen ion concentrations. Table 1 shows 

 the composition of our nine standard media. 



The contents of the nine flasks were then divided up into test 

 tubes, 10 cc. of the same standard in each, and the test tubes then 

 sterilized as before. Thus we could always work in a uniform 

 manner. The tubes were allowed to stand at least for a day at 

 room temperature in order to obtain a stable hj^drogen ion con- 



