328 The Philippine Journal of Science 1920 
Compared with Bacillus typhosus, Pseudomonas citri is very 
slightly more resistant to disinfectants, or to phenol at least, 
according to these tests. The results of Anderson and McClintic 
with B. typhosus and these with P. citri are not directly com- 
parable, however, since a 3-day-old culture was used for our 
tests, while Anderson and McClintic used a 24-hour culture of 
B. typhosus in their work. 
Table 2. — Results of exposures with 3-day-old culture of Pseudomonas 
citri in dilutions of mercuric bichloride. 
[Date of test, February 5, 1920 ; date of observation, February 7, 1920.] 
a Tube tested for P. citri, February 7 ; positive, February 8. 
A previous test had been made with dilutions up to 1 to 20,000, 
all such dilutions giving negative results. Two subsequent tests 
with dilutions of 1 to 20,000, 1 to 50,000, 1 to 80,000, 1 to 90,000, 
and 1 to 100,000 gave negative results with the 1 to 20,000 ; ex- 
posures for 2\ and 5 minutes in a dilution of 1 to 50,000 were 
positive in one case while the longer exposures were negative. 
In the other case all exposures to a dilution of 1 to 50,000 were 
positive; in both cases all exposures to dilutions of 1 to 80,000, 
1 to 90,000, and 1 to 100,000 resulted positively. Apparently, 
therefore, a 1 to 20,000 dilution of mercuric bichloride is the 
weakest dilution possible in the case of this disinfectant in order 
to secure safely bactericidal action. 
A preliminary test having given the rough limits for this dis- 
infectant, the two tests shown in Table 3 were tried, and 
they showed very close agreement. A fourth test resulted neg- 
atively for all the periods of exposure to the 1 to 300 dilution ; 
1 to 400 dilution was positive at 2-|- and 5 minutes exposure, but 
at longer exposures was negative; all of the 1 to 500 and 1 to 
600 dilutions, at all periods of exposure, were positive. There- 
