160 WINSLOW, ROTHBERG AND PARSONS 



Combining the results of tests for fermentation, gelatin lique- 

 faction and chromogenesis we obtain the subdivision of our 

 strains shown in table 8. 



PRODUCTION OF INDOL, AMMONIA AND NITRITES 



Indol production was studied in a medium containing 1 per 

 cent peptone and 0.5 per cent K 2 HP0 4 incubated at 20° for 

 ten days and tested by the para-dimethyl-amido-benzaldehyde 

 method. All tests were negative. 



Ammonia production was determined in a medium containing 

 1 per cent peptone, 0.5 per cent NaCl, 0.05 per cent K 2 HP0 4 and 

 0.01 per cent Na 2 C0 3 incubated at 30° for seven days and tested 

 with Nessler reagent. This test was suggested by Kligler (1913) 

 as perhaps of special differential value, but in the present study 

 all but 11 strains gave positive results. 



The reduction of nitrates was first tested in a medium con- 

 taining 1 per cent peptone, 0.5 per cent K 2 HP0 4 and 1 per cent 

 KN0 3 . Incubation periods of seven days, fourteen days, and 

 incubation temperatures of 30° and 37°, gave almost uniformly 

 positive results. At 30°, 8 strains only out of 180 were consist- 

 ently negative, while 19 more gave variable or doubtful readings. 



This last result seemed somewhat surprising since the senior 

 author in the Systematic Relationships of the Coccaceae reported 

 only 21 per cent of the orange cocci studied and 13 per cent 

 of the white strains as reducing nitrates. In 1908 when this 

 earlier work was done the standard method of testing for nitrate 

 reduction prescribed by the Committee on Standard Methods of 

 Water Analysis of the American Public Health Association 

 involved the use of a medium containing only 0.1 per cent pep- 

 tone and 0.02 per cent nitrate. In order to see if this difference 

 would explain the conflicting results we repeated our tests with 

 the old medium but even here we found after seven days at 20° 

 132 strains clearly positive, 38 clearly negative and 10 doubtful 

 or variable. 



Gordon (1906) in his exhaustive study of the white staphylo- 

 cocci based one of his types on failure to reduce nitrates and the 

 Winslows attributed this property to Aurococcus aureus, Auro- 



