EXACT METHOD OF CALCULATION 51 



map of the town if one cannot be obtained, make a 

 sketch-map and rule it into squares. The squares 

 should be of equal extent as far as possible, and their 

 total should include the whole area to be dealt with. 

 Begin at one corner and examine all the houses in 

 each square street by street. Write in a large note- 

 book the name of the streets and the number of each 

 house or hut, if they are numbered. If there are no 

 numbers or names, write the name of the proprietor 

 of each house and a tenant. This examination should 

 be made during the height of the mosquito season, 

 and immediately after heavy summer rains, so that 

 the estimate may be made during the period of 

 maximum density of the insects. During this ex- 

 amination a careful inspection must be made of all 

 backyards, and every cesspool should be opened. 

 The presence or absence of mosquitos or their larvae 

 should be noted, and the extent of the water surface 

 which contains them. The number of garden foun- 

 tains, water-butts, cisterns, ponds, garden puddles 

 and pools should be counted, and the presence of 

 mosquito larvae or pupae in them observed and 

 written down. 



At the end of the house-to-house examination of 

 the town the number of square metres of water sur- 

 face can be added together a water-butt may be 

 estimated as having half a square metre of water 

 surface. Then, allowing one litre of mixed oil for 

 each square metre of water surface per week, and 

 multiplying by fifty-two, the exact estimate of the 

 amount of oil required per year will be obtained. 



