828 
Journal of Agricultural Research vd. xxm, no. io 
in duplicate with 2 cc., 1 cc., 0.5 cc., 0.1 cc., and 0.01 cc. of a young 
starter. All cultures were aerated at 30° C. for four days. Sugar 
determinations were made at the end of two and four days. All cultures 
exhibited a heavy growth within two days. The sugar analysis at this 
time showed the flasks to contain the following amounts of dextrose : 
Gm. dextrose 
per 100 cc. 
Flasks with 2 cc. inoculum. o. 60 
Flasks with 1 cc. inoculum.53 
Flasks with 0.5 cc. inoculum.60 
Flasks with 0.1 cc. inoculum.48 
Flasks with 0.01 cc. inoculum.33 
The cultures gave only a trace of dextrose at the end of four days' 
incubation. The growth at this period was more vigorous in all cultures 
than the preceding one. It does not appear from these results that the 
growth of Azotobacter in such a synthetic medium could be attributed to 
stimulating factors carried over with the inoculum. The Azotobacter 
growth in the following experiments was collected by centrifuging the 
liquid culture in a Sharpies Laboratory Super-Centrifuge. The residue 
was recovered and air dried. 
FEEDING EXPERIMENTS UPON WHITE RATS 
The presence of a growth-promoting substance in this dried Azoto¬ 
bacter was tested upon white rats. The dried Azotobacter was added 
to a diet deficient in water-soluble B vitamine. The composition of the 
feed used was as follows : 
* Per cent. 
Starch. 58 
Extracted casein. 10 
Tankage. 10 
Ash. 3 
Agar. 2 
Butter. 10 
bard. 5 
Azotobacter. 2 
On April 28 six white rats were placed, in individual pens and fed 
until May 24 on a regular stock food. Upon this date three of the rats 
were placed upon the experimental feed and three upon the same feed, 
except that Fleischmann's yeast was substituted for the Azotobacter. 
The stimulating effect of each test substance is demonstrated by the 
curves in figure 2, plotted from the data obtained. It will be observed 
that during the intervals between the second and fourth weeks but little 
gain was recorded. This is attributed to the ash content of the feed. 
A new portion of feed containing new ash was prepared at this time. 
The rats fed on the Azotobacter feed show a greater comparative growth 
than the rats fed on the yeast diet. The average weights of the three rats 
fed on the Azotobacter feed is compared with the average weights of the 
three fed on the yeast food by the curves plotted in figure 2. The results 
from this experiment indicate that Azotobacter is fully as good as baker's 
yeast, if not better, as a growth-promoting substance for white rats fed 
on a diet deficient in water-soluble B. 
