17,4 Lee: Fungicides and the Citrus-canker Organism 327 
iness in such a bouillon tube indicated the presence of citrus- 
canker organisms not killed by the fungicide. Since contamina- 
tions were possible, a test was made in all doubtful cases to 
show the identity of the clouding organism. The diagnosis for 
Pseudomonas citri is very simple and consists of a characteristic 
growth on potato plugs. Bouillon tubes which were of a sus- 
picious character were therefore tested by this means to con- 
firm the presence or absence of the canker bacteria. 
Attention was mainly given to the principal fungicides which 
were found to be of possible use against canker. These were 
for the most part the standard fungicides which have been in 
use in the United States for the last decade. The results of these 
tests are best shown in the tabular form in which they are 
recorded in the card index ; the tables follow : 
Table 1 .- — Results of exposures with 3-day-old culture of Pseudomonas 
citri in dilutions of phenol. 
[Date of test, February 2, 1920 ; date of observation, February 5, 1920.] 
Exposure. 
Dilution expressed in percentage. 
0.5 
1.0 
1.5 
2.0 
2.5 
3.0 
3.5 
4.0 
4.5 
5.0 
Min. sec, 
2 30 
+ 
5 00 
+ 
7 30 
+ 
. _ 
10 00 
+ 
12 30 
+ 
a _ 
15 00 
+ 
— ■ 
a Tube tested for P. citri, February 5, 1920 ; negative, February 9, 1920. 
The test was repeated using dilution's with water of 1 to 60, 
1 to 80, 1 to 100, 1 to 120, and 1 to 140. All remained negative. 
Repeating the test with dilutions 1 to 80, 1 to 100, 1 to 120, 
1 to 140, and 1 to 160, the last-mentioned dilution showed cloud- 
iness in exposures for 24, 5, and 74 minutes, but remained neg- 
ative in the longer exposures; that is, 10, 124, and 15 minutes. 
A repetition of the test gave positive results for dilutions of 1 
to 140 for exposures of 24 and 5 minutes and for those of 1 to 
160 exposed 24, 5, and 74 minutes. The results thus agree 
closely for this disinfectant. To summarize: 1 to 120 dilution 
of phenol killed the canker bacteria in all cases, at all the 
periods of exposure employed. This was in the entire absence 
of organic matter which might precipitate or otherwise neu- 
tralize the value of the disinfectant; thus a 1 to 100 dilution 
would be considered more certain of entire disinfection. 
