"OIL" AND "LABOUR" 63 



were high ; as it came more in demand, however, its 

 price fell somewhat. 



But if it is known how much oil is required per 

 year, an estimate can be demanded from the various 

 local merchants, and the lowest tender accepted. If 

 there is any cheaper kind of oil on the market it may 

 be employed as the larvicide. " Elephant oil " is 

 quite efficacious as a mosquito larvicide, but it is 

 liable to become thick in cold weather, and will 

 require mixing with such a large quantity of refined 

 petroleum in order to spread well on the water, that 

 there is little or no saving of money. 



Facilities for the supply of oil can be obtained in 

 every town, but in some countries the presence of oil 

 depots are prohibited near dwellings. In this case 

 allowance must be made in the estimate for the 

 regular transport into the town every day or every 

 week as convenient. 



The amount of oil required per year and its cost 

 having been estimated, the next thing to do is to 

 count the number of days which were required to 

 make the house-to-house examination of the town by 

 one person. From this it is readily calculated how 

 many men will be required to visit similarly every 

 house and garden in the town once every week, 

 excluding Sundays. Then, the price of local labour 

 being known, the annual cost of the number of work- 

 men required can be readily determined. If the town 

 is a large one these workmen should be divided into 

 gangs, each controlled by an overseer or foreman. 

 Each gang should consist of three or four men, and 



