This work, carried out on a rubber estate in Malaya during 1949, was a Continuation of the trials begun in 1948 previously recorded [this Bulletin, 1949, v 46, 1116]. Full details concerning the terrain and the nature of the experiment were given in the previous publication. In 1949 the malaria rate in the area approached the rates which were customary in pre-war years, for the first time since the reoccupation of the country. The Indian population which was chosen for the experiment contains the survivors of the Japanese occupation; many had been in Siam and almost all had suffered from malaria. Treatment had been entirely lacking or very inadequate, with the result that the survivors had developed a high degree of immunity by the end of the war. These facts probably explain the low incidence of malaria in post-war years in spite of high prevalence of A. maculatus. No anti-larval measures have been carried out since 1941. Neo-premaline completely suppressed malaria in one group, the control group showing a high incidence. In other groups chloroquine, or chloroquine and pentaquine combined, given once a week, promptly brought to an end primary waves of malaria which were rising rapidly.
1. Several experiments were carried out in the field and in the laboratory with various insecticides against A maculatus. 2. Almost all the mosquitoes that came into contact with surfaces sprayed with DDT preparations died in less than 30 hours but the length of life varied with the preparation and depended on various factors that are mentioned. Control mosquitoes lived almost twice as long. 3. Gammexane Dispersible Powder (P 520) killed in a much shorter time than the DDT preparations and holds out a greater hope of success in controlling ‘A maculatus’ malaria with insecticides. 4. It is difficult to assess the value of insecticides in any one year in areas where breeding of the vector is intense. The results of long term field experiments, under strict control, are awaited. 5. Meanwhile, Mass Suppression with drugs still remains the method of choice – in this area.
In the staining of leucocytes successful use has be en made in this Department of the method described by Field (1941) in the demonstration of malarial parasites in thick films. The methylene blue solution is made up according to the formula of Hitch (quoted by Field). In the staining of these films the procedure of Field is modified so that the red cells are left intact and stained. The method as carried out is as follows. The two solutions of stain are mixed as required in the proportion of 6 drops of the methylene blue solution to 2 drops of the eosin solution and with the addition of 10 drops of buffered water at about pH 6.4. The mixture is then thoroughly shaken. The blood film is fixed with pure, acetone free, methyl alcohol for 10 seconds. The alcohol is then run off and the stain mixture applied to the slide with a pipette. Staining is continued for 10 minutes after which time the film is washed by waving about in a beaker of the buffered water at pH 6.4 for a few seconds. This method stains the leukocytes very clearly and is not subject to the several difficulties in using alcoholic solutions especially in the tropics.