Nov. 1, 1925 
Bacterial Spot of Cowpea and Lima Bean 
855 
In order to determine the tolerance of true acidity as indicated by the hydro¬ 
gen-ion concentration, a duplicate series of beef-broth tubes was made up, one 
with hydrochloric acid and the other with malic acid, and adjusted by means of 
the sulphone phthalein indicators. No growth occurred in the tubes acidified 
to P H 4.1 with either acid, but retarded growth occurred in both cases in the tubes 
acidified to P H 4.5. Good growth occurred in the Ph 5.0 tubes. Growth occurred 
in tubes rendered alkaline to P H 8.5 with either sodium hydroxide or ammonium 
hydroxide. 
TEMPERATURE RELATIONS 
The organism grows throughout a wide range of temperatures. 
Slant and plate cultures on potato agar incubated in moist chambers 
at 3° C., 9°, 12°, 15°, 20°, 23°, 27°, 30°, and 35° showed that the 
organism did not grow at 3° or 35°, but grew slowly at 9°, and 12°, 
moderately at 15°, 20°, and 35°, and rapidly at 23°, 27°, and 30°, 
with a fairly distinct optimum at 27°. 
In determining the thermal death point, water suspensions from 
agar slant cultures were subjected to 10-minute exposures to a series 
oi temperatures in a water bath and tested by loop transfers to agar 
slants {12). The thermal death-point was found to lie between 49° 
and 50° C. 
EFFECT OF FREEZING 
Heavy water suspensions from slant cultures were placed in test 
tubes, frozen in an ice-salt mixture, and held in a refrigerator. At 
intervals tubes were removed and thawed out and plates pourec^ 
The approximate number of living bacteria per cubic centimeter as 
indicated by the plate counts is shown in Table I. 
Table I .—Effect on bacteria of freezing in water 
Time frozen 
Approximate number per 
cubic centimeter 
Time frozen 
Approximate number per 
cubic centimeter 
Strain A 
Strain B 
Strain A 
Strain B 
0 a 
12,635,000 
3,192,000 
2,777,000 
27,000 
4,000 
106,714,000 
35,285,000 
13,050,000 
1,224,000 
21,000 
5 days___ 
2,000 
250 
360 
20 
149,000 
2,400 
540 
0 
hours_ 
1 day-- 
2 days... 
4 days-- -- 
8 days- 
11 days.. 
15 days_ 
« Original suspension. 
The results in Table I show that the organism is slowly killed by 
freezing in water. 
EFFECT OF SUNLIGHT 
Plates poured from tubes inoculated with a suspension of the 
organisms, and each partly shaded with black paper attached to the 
glass, were placed on a cake of ice and exposed to the afternoon sun 
for periods of varying length. Ten and fifteen minute exposures did 
not reduce the number of colonies, while 25, 30, and 45 minute ex¬ 
posures greatly reduced the number of colonies, and exposures of 
60 minntes or more resulted. b> complete sterilization. 
RESISTANCE TO DESICCATION 
The organism is very sensitive to desiccation on glass. Drops of 
a water suspension of the organisms were allowed to dry on sterile 
cover slips, and tests were made by inserting the cover slips into agar 
