D. The control groups comprise the towns of Rio Pescado and Mendoza with a small group from Los Azules. These were surveyed every month. A week after the survey was made a list of all persons found positive for malaria was given to the local village office and to the school teachers. Free quinine was provided for the use of those whose names appeared on the list of positives so that treatment was available for those who wished to take it. No attempt was made to supervise the treatment. It was left entirely to the volition of the individuals reported positive. Actually, most of the families used very little of the drug although some were very good about taking a 5-day course of the quinine as given to the members of group B. This is as near to a strictly control group as can be secured because village people are not willing to submit to blood film surveys unless a report is made and the privilege of free treatment is offered to them. The cooperation of those persons usually found negative is stimulated by providing the village with some adhesive tape, mercurochrome, argyrol, aspirin, compound cathartic pills, and such supplies. These control groups occupy an arm on the west side of Gatun Lake that compares very well with the Chagres arm of the lake on the east side. The people are fairly stable because their only contact with outside points must be by means of launch transportation to Gatun or Gamboa. The laboratory staff owes a great debt of gratitude to Canal Zone police authorities at Gamboa for providing the launch transportation required in order to make these surveys. The results of the thirteenth year's study (September 1942 to August 1943, inclusive) are presented in the tables which follow: TABLE 1.-Monthly malaria parasite rates compared with rainfall at Madden Dam 3 Surveyed every month. 4 Rainfall in inches each month. Madden Dam is near the Chagres towns. Total rainfall in inches for the 12-month period. It will be noted that the monthly parasite rate does not follow the monthly curve in rainfall in the Chagres River towns. This is true also of Rio Pescado on the left shore of the lake. Mendoza is in the hills away from important breeding centers. Los Azules is represented by a few school children in Mendoza schools. Camaron is near both fresh and salt water breeding areas. The monthly rate by no means reflects the record for an individual during the 12-month period. The cumulative record for the year provides this information and this is presented in table 2 by age groups. The table will not include information on the number of times any individual may have been found positive. TABLE 2.—Malaria parasite index by age groups, cumulative for the year 1 1 The first number in each series denotes the number of individuals examined, the second is the number found positive one or more times, and the third is the cumulative percentage of positives. These people have spent their lives in these endemic and hyperendemic malaria regions and although acquired immunity of an important degree is gained at about the age of 12 to 15 years (inactive life) yet it is unstable for those who enter an active life as laborers. When regular hours of work in a daily manner is undertaken, this tolerance or relative immunity is easily broken and the period from 15 to 25 years of age receives almost as much attention in labor camps as those below 15 years of age leading an inactive life in the villages. A new unprotected labor force of this character may start a season with a parasite rate of 20 to 25 percent but in about 6 months' time on regular duty the rate will approach two or three times that percentage. Deaths seldom occur but labor efficiency will depend on the control of malaria in the camp areas. Note the average monthly parasite rates in the various groups as compared with the cumulative rates for the year: The figures given do not include relapse or reappearance of parasites. The migratory life of these people naturally has its effect on the management of treatment and its results. TABLE 3.-Parasite index by number of times individuals were caught in the surveys 1 1 1 The first number in each series indicates the number of people examined, the second is the number found positive one or more times, and the third is the culmulative percentage of positives. Table 3 shows the difficulty in surveying regularly and treating completely all individuals during the course of a year. Note the records for the six towns that comprise the Santa Rosa station where the people have had 13 years of education in the work and where treatment is under supervision. People move away, others move in, some are temporarily employed outside, some are not available during planting and harvesting periods, school vacations intervene, there are births and deaths, and transients come from a distance to remain 2 weeks for diagnosis and free treatment. All of these things affect the results obtained. We consider the stable populations of the several survey groups to be as follows: Atabrine group-Chagres River towns (the year's records show 334) 186 159 88 Control group-Mendoza 1 and Los Azules (the year's records show 371) _ 102 98 633 Total of all groups surveyed (the year's records show 1,418) - - - 1 There are 32 people who live in the immediate limits of the small village of Mendoza in the hills and the remainder represent school children drawn from a radius of 4 miles. Vacation periods for this school center amount to about 4 months. TABLE 4.-Percentage of individuals caught in the surveys during the year TABLE 5.-Species of parasites found from 1 to 7 times in certain individuals during the year but not necessarily in successive surveys. They may represent new infections, relapses, or the reappearances of parasites, mixed infections, and, perhaps in some instances where parasites are few in number, technical mistakes in the identification of parasites E denotes P. falciparum. T denotes P. vivar. Q denotes P. malariae. The cases of clinical relapse, those complaining of acute or mild symptoms of malaria associated with parasites in their blood films, were fewer than usual during the past year. The rates for the various groups were, for the atabrine group, 10.8; for the quinine group, 24.6; for Rio Pescado, 50.0; for Mendoza and Los Azules, 21.0; for Camaron, 42.7. The consolidated records show a single relapse in 78 persons, 2 relapses in 33, 3 relapses in 13, 4 relapses in 7, and 5 relapses in 4. According to species of parasites found, they occurred as follows: P. falciparum 83 (61.4 percent); P. vivax 38 (28.1 percent); P. malariae 14 (10.3 percent). Many of the so-called relapses recorded for Rio Pescado, Mendoza, and Camaron represent insufficient treatment of chronic malaria in control towns. In the quinine and atabrine supervised groups a single relapse occurred in 18 people, 2 relapses in 5 people, 3 relapses in 3 people, and 4 relapses in 1 person. According to species they classified as P. falciparum 16 (59.2 percent); P. vivax 8 (29.6 percent); P. malariae 3 (11.1 percent). However, during the year 163 blood films contained P. falciparum so that the relapse rate was 9.8 for that species, 49 films contained P. vivax and the relapse rate for that species was thus 16.3 while 17 films showed P. malariae so that the relapse rate there was 17.6. Most of the relapse rate was in the benign species but general opinion seems to underestimate the importance of relapse in P. falciparum infections. TABLE 6.-Species incidence of the malaria parasites, cumulative for the year TABLE 7.-Malaria survey of babies from birth to 12 months of age The measure in use for revealing new infections in the villages is the baby during its first 12 months of life. Only one baby was found positive in the towns where treatment with atabrine and quinine was |