HEMOLYTIC STAPHYLOCOCCI 



19 



and thus the figures are kept low ; whereas in peptone broth, the amino- 

 acidity figures increase rapidly due to the greater amounts of peptone 

 present. 



Production of Ammonia. This test was performed for a double 

 purpose : In the first place, it was interesting to determine what 

 happened to the amino acid formed, and in the second place, to 

 determine whether any differentiation could be made on this basis. The 

 amount of ammonia formed was measured daily for 5 days after incu- 

 bating at 37 C. The medium employed was composed of \% peptone 

 and 0.05% K 2 HPO 4 . The tubes were sealed with paraffin to prevent 

 the escape of ammonia. The determination was made with Nessler 

 reagent, and the cultures were matched against a known standard by 



TABLE 9 

 AMMONIA FORMATION 



Figures represent mg. of NHs as nitrogen per 100 c c of culture. 



means of the Dubosq colorimeter. From table 9 it will be seen (1) that 

 all the cultures produce ammonia, and (2) that amino-acidity and 

 ammonia formation are simultaneous processes. Winslow, Rothberg 

 and Parsons report positive ammonia formation in all but 11 strains 

 out of 180 studied. 



Reduction of Nitrates. Gordon 30 and Winslow, 28 Rothberg and Parsons M 

 found that nitrate reduction by staphylococci was a more or less general char- 

 acter. Winslow and Winslow 28 reported only 21% aureus and 13% albus 

 reducers. Kligler's study showed 7 out of 11 aureus and only 1 out of 12 

 albus reduced nitrates. The more recent work of Winslow, Rothberg and 

 Parsons w had the advantage of better technic and should have the greatest 

 weight. 



