[Vor. 1 
58 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
in both tests. This stain, as may readily be seen, is of no 
differential value here, for, although the salivary cocci react 
positively throughout, both positive and negative reactions 
occur among the air and skin forms. bs 
The production of indol among coccus forms is very uncom- 
mon. Of the salivary cocci under observation, none produced 
indol, and of the air and skin forms only one from each group 
produced it. The change of color in neutral red broth is, 
apparently, more frequently brought about by the salivary 
cocci than by the air and skin forms, but this difference is not 
sufficiently well marked to be of differential value. Of the 
20 salivary cocci, 12 produced fluorescence, whereas only 1 of 
the air and none of the dermal forms produced this change. 
All of the forms under observation reduced nitrates to ammonia. 
Of the salivary forms, 14 out of 20; of the air cocci, 5 out of 18; 
and of the skin cocci, 5 out of 6, reduced nitrates to nitrites. 
It thus appears that the reduction of nitrates to ammonia 
is very common among members of the Coccacee, but that the 
reduction to nitrites only is variable and not characteristic 
of any one type. 
The average amounts of gelatin liquefied after 30 days' 
growth at 20°C., are as follows: by the salivary cocci, 2.8 се.; 
by the air forms, 1.9 се.; and by those of the skin, 1.4 cc.  Fif- 
teen out of 20 of the salivary organisms, 15 out of 18 of the air 
forms, and 4 out of 6 of the skin cocci, liquefied gelatin. Sum- 
ming up the results obtained from the experiments on gelatin 
liquefaction, it is to be.noted that, in general, the salivary 
cocci liquefy gelatin more readily than do the air or skin forms, 
but aside from this it is apparent that there is nothing to warrant 
the use of gelatin as a differential medium. 
The results of the experiments on vigor of surface growth 
on agar slopes at 20°C., and 37°C., are given in table п. While 
it may be said, in general,—from the results given in this 
table—that the salivary cocci grow somewhat more vigor- 
ously at 37°C. than at 20°C., the air forms better at 20°C. 
than at 37°C., and the skin organisms about equally well at 
the two temperatures, the differences are not sufficiently pro- 
nounced to impart to the factor of vigor of surface growth 
any marked value as a differential characteristic. 
