BACTERICIDAL INFLUENCE OF FLOUR 
Experiment 3. Conditions exactly the same as in experiment 2. 
When cultures were 
made 
Dilution 
No. of colonies on 
plate 
No. of bacteria per c.c. 
Immediately 
i : 10,000 
282 
2,820,000 
1 day 
1 : 100 
0 
Less than 100 
3 days 
1 : 1 
2 
2 
5 days 
1 : 1 
O 
0 
6 days 
1 : 1 
O 
0 
In these experiments the f>\ typhosus disappears more rapidly than in the 
unfiltered emulsions. The reason may be that the filtering removes some of the 
nutriment contained in the mixture of flour and water. 
An attempt was next made to see if flour could he sterilized and yet possess 
any bactericidal effect. Ten grammes of flour were sterilized in flowing steam for 
twenty minutes on three successive days. One hundred cubic centimetres of sterilized 
water were added to the ten grammes of sterilized flour, and the mixture was 
inoculated with B. typhosus. The experiment is too long to give in tabular form, 
because there was no decrease in the number of organisms for thirty-three days, and 
it was recovered as late as the 127th day after inoculation. 
Two explanations might be given of this result :— 
1. The heating may have destroyed the bactericidal substance. 
2. The heating may have changed the flour so that it formed better 
food for the bacteria. 
To throw some light on this problem, a series of experiments were made by 
filtering a ten per cent, emulsion of flour in sterilized water through a sterilized 
Pasteur-Chamberland filter. The filtrate was heated to boiling, and inoculated 
with B. typhosus (see experiments 4 and 5). 
Experiment 4 
When cultures were 
made 
Dilution 
No. of colonies on 
plate 
No. of bacteria per 
c.c. 
Immediately 
I : 1 
CO 
00 
2 days 
I : 1 
20 
20 
4 days 
1 : 1 
O 
O 
5 days 
1 : 1 
O 
O 
