14 
BULLETIN 782, U. S. DEPARTMENT OF AGRICULTURE. 
tion. It will be noted that in medium A, 25 cultures showed a 
distinct fermentation of dextrose, the hydrogen-ion concentration 
in most cases going from P H 6.9 (control) to P H 4.5, a few cultures 
reached about P H 6.0, and only 19 cultures changed from P H 6.9 to 
P H 6.5 or lower. These cultures it was believed fermented dextrose 
but were called plus or minus. 
Table 5. — Results of fermentation of dextrose in synthetic media with different buffer 
contents. 
Culture 
No. 
Medium A. Medium 13. Medium C. 
Dex- 
trose 
fer- 
men- 
ta- 
tion. 
Control . . 
10 
12 
31 
49 
61 
62 
66 
72 
73 
101 
102 
103 
104 
105 
106 
107 
108 
111 
112 
113 
114 
116 
117 
118 
119 
120 
121 
122 
123 
124 
125 
126 
128 
Dex- 
trose 
fer- 
men- 
ta- 
tion. 
Ph. 
o. o 
5.4 
6.2 
5.4 
7.2 
7.2 
7.2 
7.2 
7.2 
6.2 
7.2 
7.2 
7.2 
7.2 
7.2 
7.2 
7.2 
5. 5 
7.2 
7.2 
6.0 
5.5 
7.2 
7.2 
7.2 
7.2 
7.2 
5. 5 
6.2 
7.2 
4.5 
7.2 
7.2 
7.2 
7.2 
4.8 
Dex- 
trose 
fer- 
men- 
ta- 
tion. 
Sum- 
mary 
of 
dex- 
trose 
fer- 
men- 
ta- 
tion. 
Culture 
No. 
Medium A. Medium B. Medium C. Sum- 
mary 
of 
dex- 
trose 
Dex- 
trose 
fer- 
men- 
ta- 
tion. 
0.9 
Control. 
130 
131 
132 
133 
134 
135 
136 
137 
138 
139 
140 
141 
142 
143 
144 
145 
• 146 
147 
303 
314 
317 
319 
321 
322 
325 
326 
340 
353 
354 
356 
301 
3G2 
Ph. 
7.2 
Dex- 
trose 
fer- 
men- 
ta- 
tion. 
6.9 
_ 
7.2 
6.6 
± 
7.2 
6.6 
± 
7.2 
4.5 
+ 
6.2 
4.5 
+ 
6.2 
6.7 
_!_ 
7.2 
6.5 
± 
7.2 
4.5 
± 
5.0 
6.6 
± 
7.2 
6.9 
- 
7.2 
6.5 
± 
7.2 
4.5 
+ 
6.0 
6.9 
7.2 
4.5 
+ 
5.4 
6.6 
± 
7.2 
6.9 
_ 
7.2 
6.6 
± 
7.2 
6.9 
7.2 
6.9 
— 
7.2 
6.9 
- 
7.2 
5.6 
+ 
6.3 
6.9 
— 
7.2 
6.2 
+ 
6.5 
6.2 
+ 
6.3 
6.2 
+ 
6.4 
6.2 
+ 
6.5 
6.2 
+ 
6.5 
6.9 
7.2 
6.9 
— 
7.2 
6.9 
- 
7.2 
6.2 
+ 
6.5 
6.0 
+ 
6.4 
6.3 
+ 
6.2 
Ph. 
3 
r 5.0 
5.3 
5. 
5.0 
Dex- 
trose 
fer- 
men- 
ta- 
tion. 
fer- 
rnen- 
ta- 
tion. 
Medium B, while having less buffer than medium A, contained 
also less dextrose, and in it only 25 cultures showed a positive 
fermentation. Medium C was then tried and it contained the same 
amount of dextrose as medium A but half the sodium-ammonium 
phosphate. As this medium had considerably less buffer than 
medium A, it was expected that the cultures showing only a slight 
change in P H in medium A would show a much larger change in 
medium C. This was found to be the case, as is shown in the table. 
