282 
MALARIA 
is confirmed by the figures in Table X, 
which show a steady increase of “heavy 
infections” among our treated population. 
Whatever may be the cause of the cyclical 
variations which occur in the malarial para¬ 
site rate, their existence must be considered 
in evaluating the results of control mea¬ 
sures. By an unfortunate chance, our 
initial surveys made in 1929 showed high 
rates, and much of the success of our efforts 
has been referred back to these high rates 
as a base-line. If, however, we had made 
our initial surveys in September 1930, we 
would have been much less encouraged by 
our results, as the 1930 figures, 16.2 per 
cent, were low. In fact, they were a frac¬ 
tion lower than the average monthly rate 
for the 12 months ending August 1932, 
after two years of treatment with quinine 
and plasmochin (Table 1 of our second 
year’s observations, 1932). 
“In order to reach satisfactory con¬ 
clusions in regard to the value of anti-ma¬ 
laria measures, the natural trend of the 
disease must be observed over a period 
sufficiently long to pass through several 
cycles of the disease. Otherwise, what may 
appear to be a success may be only a swim¬ 
ming with the tide. In order to correctly 
evaluate a drug, it should be administered 
over a period long enough to include one 
of the cyclical upswings of the malaria rate. 
Only if it is successful under these condi¬ 
tions can it be considered of any value in 
community malaria control or prevention. ’ ’ 
The value of our observations is enhanced 
because they have been made over a period 
of time long enough to encounter a number 
of normal cyclical variations. There has 
been a steady diminution in average annual 
parasite rate, as determined by monthly 
surveys in the treated groups. As shown 
in Table I the average annual rate for these 
groups was 21.6 per cent, in the first year 
of treatment. Nine years later, in 1939- 
1940 this rate was reduced to 12.1 per cent. 
A comparable decrease was not noted in 
the control groups, so far as figures for 
these groups are available. We believe that 
the reduction in the annual parasite rate 
in our treated groups is a fair measure of 
the success of our work. 
Summary 
1. This report deals with an experiment 
in the control of malaria with drugs alone, 
conducted in a rural region of high en- 
demicity in Panama, where no anti-mos¬ 
quito measures were used. The experiment 
has extended over a period of 10 years. 
The population concerned were native Pan¬ 
amanians, with a large negroid strain, liv¬ 
ing in six villages located on the banks of 
the Chagres River between Madden Dam 
and the eastern boundary of the Canal 
Zone; and a control group living about five 
miles away on Madden Highway. Breeding 
of A. albimanus, the principal malaria 
vector, was abundant in the aquatic vege¬ 
tation along the river-banks and in the 
many lagoons and backwaters near the 
towns. Such breeding became extremely 
abundant at periods of low water, caused 
by the impounding of water behind Madden 
Dam, which resulted in slow current and 
semi-stagnant conditions in the river. 
2. During the entire period of our studies, 
no correlation between the monthly ma¬ 
larial parasite rate and monthly rainfall 
was noted. The annual rainfall varied 
from 73.32 inches to 123.15 inches, with an 
annual average of about 100 inches. 
3. The population involved in our studies 
was divided into three groups, two of which 
were treated, and the other used as a con¬ 
trol. In all our work, only those indi¬ 
viduals who were found parasite-positive, 
as indicated by examination of blood-films, 
were treated. Mass treatment of the popu¬ 
lation was not attempted at any time. The 
control group was provided with quinine 
sulphate, which was taken voluntarily, with 
no attempt at supervision of treatment. 
This method was used in the control groups 
throughout the course of the experiment. 
Prom September 1930 to September 1932, 
the two treated groups were given quinine 
sulphate alone, or with plasmochin. In 
September 1932, one group was treated 
with atabrine 0.1 gram 3 times a day for 
5 days, followed 2 days later by plasmochin 
simplex 0.01 gram twice a day for 5 days. 
The other group was treated with quinine 
sulphate (tablets) 0.972 grams a day for 5 
