278 
MALARIA 
TABLE VI 
Individuals Surveyed 12 Consecutive Months* 
Chagres 
New San Juan 
Totals 
Controls t 
Ages 
Ex- 
Posi- 
Posi¬ 
Ex- 
Posi- 
Posi¬ 
Ex¬ 
Posi¬ 
Posi¬ 
Ex¬ 
Posi¬ 
Posi¬ 
amined tive 
tive 
amined tive 
tive 
amined 
tive 
tive 
amined 
tive 
tive 
years 
No. 
No. 
% 
No. 
No. 
% 
No. 
No. 
% 
No. 
No. 
% 
0-5 
165 
65 
39.4 
114 
49 
43.0 
279 
114 
40.8 
228 
70 
26.2 
5-10 
135 
71 
52.6 
69 
41 
59.4 
204 
112 
54.9 
1020 
385 
37.7 
10-20 
69 
45 
65.2 
38 
28 
73.7 
107 
73 
68.2 
1028 
415 
40.3 
20—40 
63 
23 
36.5 
50 
24 
48.0 
113 
47 
41.6 
293 
67 
22.8 
40-60 
50 
19 
38.0 
15 
6 
40.0 
65 
25 
38.4 
119 
35 
29.4 
Over 60 
15 
5 
33.3 
17 
5 
29.4 
32 
10 
31.2 
25 
4 
16.0 
Totals 
497 
228 
45.9 
303 
153 
50.5 
800 
381 
47.6 
2713 
976 
36.0 
* Period covered September 1935 to and including August 1940. 
+ Controls: Madden Highway schools, 4 surveys; Chilibre (town on Madden Highway), 1 survey; 
Bio Pescado, Gatun Lake shore, 1 survey. 
denee is highest in ages 5 to 20 and that 
those above 60 years of age, who have spent 
their lives in these highly endemic centers, 
are not immune to malaria. 
In addition to the figures given above, 
the Buenos Aires schools (on the Madden 
Highway) were examined 4 times (Oct. 
1939, Jan., May and Aug. 1940). The num¬ 
ber of positives found was 203. No treat¬ 
ment was given in this area, except quinine 
sulphate, which was provided for the posi¬ 
tives, to be used if they so desired. There 
was no supervision of treatment. The re¬ 
sults of the survey show that of the 203 
TABLE VII 
Individuals (405) Positive for Malaria who 
Were Surveyed Regularly for 12 Con¬ 
secutive Months. Period of Sept. 1, 
1935-Aug. 31, 1940 
Times 
positive 
Chagres 
New San 
Juan 
Chilibre 
Total 
1 
124 
75 
2 
201 
2 
54 
35 
5 
94 
3 
27 
18 
5 
50 
4 
12 
13 
2 
27 
5 
8 
7 
2 
17 
6 
1 
4 
4 
9 
7 
2 
3 
0 
5 
8 
0 
0 
1 
1 
9 
0 
0 
1 
1 
Totals 
228 
155 
22 
405 
positives, 115 were positive once; 55 twice; 
23 three times; and 10 four times. Thus 
88, or 43.3 per cent, were positive from 2 
to 4 times. 
We believe that the larger proportion of 
positive findings is due to relapse, not to 
new infections. This is well shown in those 
who were repeatedly positive over long 
periods. These repeaters were certainly 
less tolerant to malaria than others living 
in the same area, for they kept a high para¬ 
site rate even though they were subjected 
to treatment at frequent intervals. Certain 
families, regardless of the location of their 
homes, show very low tolerance to the 
disease, and these people defeat our efforts 
to attain a further reduction in malarial 
parasite rates. 
Mixed infections are no doubt more 
common than is indicated in Table VIII, 
as it is often necessary to examine blood- 
films made on successive days to discover 
such infections. Table VIII shows that P. 
falciparum infections constitute the major¬ 
ity of our positives and that P. vivax and 
P. malariae infections are more common in 
the Madden Highway groups than in the 
Chagres River villages. 
The crescent rates among P. falciparum 
infections seem very high, yet during 9 
years of our observations only about 43 
heavy crescent-carriers were found in the 
