PACIFIC SCIENCE, Vol. IV, July, 1950 
176 
3-6 are concerned with the antibacterial ef- 
fects of the plant extracts and present this 
information: (1) the scientific name of the 
plant; ( 2 ) the part of the plant yielding the 
extract being tested; (3) the pH of the ex- 
tract; and (4) the diameters of the zones of 
inhibition, measured in millimeters, devel- 
oped against the different test organisms. 
Wherever, by intention or by accident, a par- 
ticular bit of information was not obtained, 
a question mark (?) indicates this fact; the 
words "not tested” mean that the organism 
(usually Ps. aeruginosa) was not used in the 
testing of a particular extract; the symbol 
''qns” means "quantity not sufficient” to ob- 
tain a pH determination; the symbol "O” 
means no apparent zone of inhibition. 
The tests showed that very acid buffer solu- 
tions (pH 3.0 and 4.0) are only moderately 
effective in their ability to inhibit growth of 
the test organisms, and that solutions with 
pH values ranging from 5.0 to 8.0 had no 
effect at all. 
This is an observation that has direct bear- 
ing upon the results disclosed in this study 
of extracts from Hawaiian medicinal plants, 
for, in a number of instances — as will be seen 
from Tables 3 to 6- — it was found that the 
zones of inhibition produced by the extracts 
were far greater than were the zones of in- 
hibition produced by the buffer solutions hav- 
ing the same pH values as did the extracts 
being tested. In those extracts having a pH 
more acid than 3.0, moreover, the degree of 
inhibition achieved by the extracts was sig- 
nificantly greater than that achieved by the 
buffer solution of pH 3.0. On the other hand, 
as the list on page 179 shows, there were also 
many extracts of moderate ac’dity which ex- 
erted no inhibitory effect at all upon the test 
bacteria. 
The implication here is that, in those plant 
extracts which are potent in their degree of 
inhibition of the test bacteria, it is not so 
much the mere pH of the extract that is the 
effective antibacterial agent, but rather the 
TABLE 3 
Extracts Which Exhibit Very Effective Antibacterial Properties 
( with zone of inhibition 20 mm. or more in diameter) 
NAME OF PLANT 
PART OF PLANT 
PROVIDING EXTRACT 
pH 
OF EX- 
TRACT 
DIAMETER OF ZONES OF INHIBITION 
(IN MM.) 
M. Ps. aeru- 
pyogenes E. coli ginosa 
Dicranopteris linearis 
leaves and stems 
4.6 
21 
0 
13 
Alpinia purpurata 
leaves 
6.6 
10 
22 
20 
Acacia Koa 
stems 
5.6 
20 
0 
0 
T amarindus indica 
ripe fruit 
2.4 
30 
30 
not tested 
fruit, aqueous extract 
p 
25 
24 
not tested 
green fruit 
2.5 
25 
26 
25 
Citrus aurantifolia 
fruit 
2.6 
27 
25 
25 
Hura crepitans 
flowers 
4.5 
20 
14 
( discolored ) 
Pas si flora edulis f. flavicarpa 
green fruit 
3.4 
27 
28 
30 
ripe fruit 
3.7 
22 
22 
20 
Passi flora foetida var. 
fruit 
4.2 
15 
32 
15 
Pas si flora sp. 
flowers 
5.6 
10 
35 
10 
Punica Granatum 
whole fruit* 
3.5 
20 
20 
15 
fruit-rind 
3.7 
22 
0 
13 
Eugenia malaccensis 
seeds 
4.7 
25 
0 
0 
bark* 
5.9 
20 
0 
not tested 
leaves* 
5.4 
20 
0 
not tested 
Metrosideros macropus 
stems 
4.9 
30 
8 
8 
Psidium Guajava 
leaves and flowers 
p 
20 
10 
not tested 
See Table 6. 
