664 I. J. KLIGLER 



A. Effect of different concentrations of peptone on the nitrogen 

 utilization of certain intestinal bacteria. The best measure of the 

 degree of bacterial metabolism in nitrogenous media is the 

 amount of ammonia liberated. This criterion was therefore 

 used. The technique was, briefly, as follows: 



Simple solutions of peptone in distilled water containing vary- 

 ing amounts of peptone and 0.5 per cent glucose were used. Two 

 series were run; one with Witte's and the other with an American 

 peptone. The different lots of media from each peptone were 

 made at the same time, flasked, and autoclaved under the same 

 conditions. Inoculations were made from young cultures and 

 the flasks incubated at 30° C. for seven days. One lot of Witte 

 peptone was incubated for five days, but this period was found 

 insufficient. 



The ammonia determinations were made according to the 

 Folin micro method. First, 5 cc. of the culture were used but 

 later 10 cc. were found more satisfactory, due to the small 

 amounts of ammonia present. The period of aeration was 

 twenty minutes. The ammonia was caught in 10 cc. -^6 sulphuric 

 acid and the excess acid titrated with ~ Na(OH). 



The effect of different concentrations of peptone is evident 

 from the results of this experiment. It is, of course, possible 

 that the greater ammonia production with the higher concen- 

 tration of peptone is due merely to the favorable action of the 

 increased amount of buffer in keeping down the hydrogen ion 

 concentration. That the concentration of the peptone is in 

 itself an important factor, is however indicated by the different 

 results obtained with different types of bacteria. B. typhi, for 

 instance, produced no ammonia in the 0.5 per cent peptone in 

 one medium and a negative quantity in the other, while in the 

 higher concentrations small amounts were obtained, though less 

 than in the sugar-free control. B. coli and B. cloacae, etc., give 

 increasing amounts of anunonia with the increasing concentra- 

 tion of peptone; but in all cases the amount still remains lower 

 than in the sugar-free control. 



The results, on the whole, indicate that the concentration of 

 peptone is an appreciable factor when the concentration of glu- 

 cose is moderately low. Attention may also be called in passing 



