16 BULLETIN 782, U. S. DEPARTMENT OF AGRICULTURE. 
The results of the fermentation of dextrose in these simple synthetic 
media were so different from the fermentation in the complex extract- 
broth medium that the results are compared in Table 7. In the 
dextrose-broth medium incubated for 7 days, 15 cultures showed a 
production of at least 1 per cent normal acid and on this basis 10 
cultures showed a dextrose fermentation in the same medium after 
21 days' incubation, yet in the synthetic medium 44 of the 68 cultures 
fermented dextrose. The results indicate very clearly the inac- 
curacies which may occur in the study of the fermentation of test 
substances in complex media. 
GALACTOSE. 
The alkali-forming bacteria fermented galactose in a manner nearly 
identical with dextrose. Practically all the cultures which fermented 
dextrose fermented galactose and, in fact, reached about the same 
hydrogen-ion concentration in the synthetic medium. 
LACTOSE, SACCHAROSE, AND RAFFINOSE. 
Lactose is not fermented in the ordinary beef-extract medium 
when measured by the usual titration methods or by the change in 
hydrogen-ion concentration. The assumption that the alkali-forming 
bacteria are nonlactose fermenters based on results of the fermenta- 
tion of the sugar in ordinary media is quite incorrect, as is shown in 
Table 8. It was found that 11 of the cultures showed a slight change 
in hydrogen-ion concentration in synthetic medium A. Medium A 
and medium C were the same as previously described except that 
lactose was substituted for dextrose. The slight fermentation of 
lactose was more clearly indicated by the results obtained with 
medium C. There is included also in the table the reaction of skim- 
milk cultures of the organisms after 7, 14, and 30 days' incubation 
at 30° C. In every. case the acidity decreased during the first 7 days 
and then increased. After 14 days the acidity in all but 3 cultures 
was higher than on the seventh day, while in 30 days all the cultures 
showed a marked increase in acidity compared with that of the 
seventh day. 
The acid formation, which is probably secondary in milk, correlates 
perfectly with the cultures which showed a slight fermentation of 
lactose in the synthetic media. All the cultures which showed no 
indication of fermentation of lactose in the sodium-ammonium-phos- 
phate medium failed to show any secondary acid formation in milk 
during a period of 30 days. 
Saccharose was found to be fermented by only 2 of the cultures, 
Nos. 31 and 72. In a synthetic medium these change the reaction 
from P H 7.1 to P H 6.5 and 6.6, respectively. This indicates only a 
slight fermentation. 
Raffinose was not fermented by any of the cultures even when 
several of the different media were used. 
