A Method of Anti-Larval Oiling for Rivers

Introduction.?During the monsoon in Assam, the rainfall is characterized by spells of heavy downpour followed by intervals, short or long, of hot, dry weather. The result of this irregularly distributed rainfall is that the permanent rivers and streams sometimes flow slowly and sluggishly, and at other times, after heavy rains, are converted into wide, deep, rapidlyflowing channels loaded with silt and debris. The velocity of these streams and rivers therefore varies considerably. In a previous article, the writer has detailed experiments dealing with these velocities. It was found that velocities exceeding 2.04 miles per hour were sufficient to wash out the larval stages of Anopheles minimus which is the principal, almost the only, vector of human malaria in Assam. Similar results were obtained by De Jesus in the Philippines. Where, however, there