1920] 
CHAMBERS—BACTERIAL INHIBITION BY METABOLIC PRODUCTS 261 
and the subcultures were then observed as new cultures. The 
points of maximum growth for the different subcultures in order 
are 557,000,000, 428,000,000, 342,000,0C0, 264,000,000, and 
274,000,000 bacteria per cc., so that the subcultures fall in a 
regular series of decreasing maximum growths, with the excep- 
tion of Culture 4 whose maximum might have occurred unob- 
served between 84 and 96 hours. "There is nothing distinctive 
in the changes in hydrogen ion concentration, each subculture 
producing acid to P, 4.9 in 24 to 36 hours. It would seem, 
then, from this series of subcultures that some factor besides 
hydrogen ion concentration caused an inhibition of the growth, 
increasing with the age of the culture. 
To determine the influence of the exhaustion of the medium 
as a factor in the inhibitory action shown in fig. 2, another simi- 
lar series was observed. Four subcultures of 200 cc. each were 
removed from a parent culture at 96 hours and treated in differ- 
ent ways. All were readjusted to approximately neutral with 
N/1 NaOH. In addition 50 ce. of plain bouillon condensed 5 
times was added to No. 2 (200 cc.), making a total volume of 
250 cc. No. 3 received 50 cc. of the condensed bouillon and 
1 per cent dextrose. No. 4 received the same nutrients as No. 3 
and was then sterilized for 15 minutes at 120? C. to kill any 
"autotoxin" or inhibitory enzymatie substance, and reinocu- 
lated as a new culture. The results are contained in table 11 
and fig. 3. The changes in hydrogen ion concentration are 
very uniform, falling on almost the same line, an increase until 
Py 4.9 is reached in 48 hours. The exhaustion of the medium 
is shown, however, by the increased growth both in the culture 
with the bouillon replenished and in the replenished bouillon with 
dextrose added. The addition of dextrose shows almost no 
advantage over the addition of concentrated bouillon alone, 
so that dextrose is not considered an important factor at this 
time. Acid production from Py 7.3 to 4.9 in Subcultures 1 and 2 
where the dextrose was not replenished shows that all the dex- 
trose had not been fermented in the parent culture at 96 hours. 
The maximum in Subculture 3 (table rrr) of 545,000,000 bacteria 
per cc. compares very favorably with 557,000,000 in Subcul- 
ture 1 of table 1, so that it would appear that the exhaustion 
of the nutrients contained in the plain bouillon was a very im- 
