330 The Philippine Journal of Science 1920 
One other test was in such close agreement with the results 
shown in Table 4 that no further repetitions were made. A 
1 to 50 dilution of this emulsion was used in the field. Such a 
dilution, according to these data, would seem to be entirely safe 
in the absence of any organic matter which would precipitate 
or otherwise neutralize the action of the disinfectant. 
Table 5. — Results of exposures with 3-day-old culture of Pseudomonas 
citri in dilutions of formalin. 
[Date of test, February 3, 1920 ; date of observation, February 6, 1920.] 
Exposure. 
Dilution. 
1 to 
200. 
1 to 
180. 
1 to 
160. 
1 to 
140. 
1 to 
120. 
1 to 
100. 
1 to 
80. 
1 to 
60. 
1 to 
40. 
1 to 
20. 
Min. 
sec. 
2 
30 
+ 
+ 
+ 
+ 
+ 
+ 
» + 
+ 
+ 
— 
5 
00 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
— 
— 
7 
30 
+ 
+ 
+ 
+ 
+ 
“+ 
+ 
— 
— 
- 
10 
00 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
— 
— 
— 
12 
30 
+ 
+ 
+ 
+ 
+ 
+ 
b— 
— 
— 
— 
15 
00 
+ 
+ 
+ 
+ 
a + 
C + 
— 
— 
— 
— 
a Exposure tested, February 6 ; positive, February 7. 
b Exposure tested, February 5 ; negative, February 8. 
c Exposure tested, February 7 ; positive, February 8. 
Tests with formalin dilutions were made repeatedly in as 
much as there was a slight degree of variation in the results 
from exposures of dilutions of 1 to 40, 1 to 60, and 1 to 80. 
Formalin 1 to 100 at no period of exposure resulted in the killing 
of the canker bacteria. In one test all exposures at a dilution 
of 1 to 80 gave similar positive results, although in other tests 
the exposures for 10, 12i, and 15 minutes were negative. A 
dilution of 1 to 60 formalin in all tests failed to kill the canker 
bacteria in 2\ minutes; in one instance also it failed to kill 
after an exposure of 5 minutes. Two instances also occurred in 
which 1 to 40 formalin failed to kill at exposures of 2% minutes 
although negative results were always obtained at 5-minute 
exposures. Such variations were probably due to some extent 
to variations in the content of the commercial formalin solutions 
used in the different tests. In any event it appears safe to 
say that, in orchard practice, no formalin solution more dilute 
than 1 to 20 is a safe disinfectant against the canker bacteria. 
In the writer’s experience a dilution of 1 to 80 was the strongest 
that trees of Citrus maxima, C. hystrix, C. nobilis, or C. sinensis 
would stand without serious burning, under tropical conditions. 
Trees of C. limonia or C. aurantifolia are much more susceptible 
