Antibacterial Properties of Plants — Bushnell, et al. 
175 
for study was limited, too. Many of those 
which played an important part in the kahu- 
na's pharmacy were difficult to obtain even 
in their day, and are even harder to find now. 
Some of them have become extinct or inacces- 
sible, and most of the plants grow in habitats 
so far removed from the laboratory that they 
are not conveniently available for study. 
The number of species of bacteria we could 
use to determine the "spectrum” of activity 
of a plant — that is, the range of its effective- 
ness as an antagonistic agent for the different 
species of bacteria-™ was so limited by the 
time and facilities at our disposition that we 
could not possibly expose all of the different 
micro-organisms which might have assailed 
a susceptible Hawaiian. 
Nonetheless, the determination of the anti- 
bacterial effect of extracts of the different 
medicinal plants offers the one feasible means 
for assaying them in the absence of human 
cases to study or of laboratory animals to 
experiment upon. 
Before very many plants were tested it be- 
came evident that there were great variations 
in effectiveness of the plant extracts obtained 
from the different species of plants, and, in- 
deed, often among extracts obtained from the 
several parts of the same plant. There was 
also considerable variation in effectiveness of 
many of the extracts against the several dif- 
ferent test organisms. 
It is difficult, then, to tabulate easily the 
results obtained in this study. We have finally 
decided to do what the Hawaiians did, and 
to treat each separate part of a plant as an 
entity of its own — if only because we found, 
as they did, that the different parts of the 
plant vary astonishingly in their pharma- 
cological properties. 
We set some arbitrary standards of effi- 
cacy, basing these standards upon the Oxford 
group’s definition of a unit of penicillin — 
that amount of penicillin which gives an in- 
hibition zone 24 mm. in diameter — and the 
work of Sanders et al. (1945) in appraising 
the antibacterial substances in plants col- 
lected in Indiana. Four categories were estab- 
lished, based upon the diameters of the zones 
of inhibition obtained with the plant extracts 
against any one of the test organisms: 
1. Very effective: zones more than 20 
mm. in diameter 
2. Moderately effective: zones between 
10 and 20 mm. in diameter 
3. Slightly effective: zones less than 
10 mm. in diameter 
4. Ineffective: no apparent zone of 
inhibition 
The summarized data of our studies are 
presented in Tables 2-6 and in a simple list- 
ing of the ineffective extracts (see p. 179). 
Table 2 presents the results of the studies with 
buffer solutions of different pH values. Tables 
TABLE 2 
Effect of Buffer Solutions of Different pH upon the Test Bacteria 
TEST ORGANISMS 
Micrococcus pyogenes var. aureus 
Escherichia coli 
Pseudomonas aeruginosa . 
Salmonella typhosa 
Salmonella montevideo 
Salmonella schottmuelleri . 
Shigella paradysenteriae BH . 
Shigella paradysenteriae III-Z 
ZONES OF INHIBITION (IN MM.) 
ACHIEVED BY 0.2 ML. OF 
BUFFER SOLUTIONS 
pH 3.0 pH 4.0 pH 5.0, 6.0, 8.0 
10 0 0 
10 8 0 
12 8 0 
8 0 0 
10 0 0 
12 8 0 
13 0 0 
13 0 0 
