133 



other 1,756, this would make in all 578 basins breeding, surely 

 enough to make quite a disturbance if breeding were allowed to 

 emerge. 



Satisfied that the question warranted further investigation, 

 we proceeded as follows : I will quote from my report — 



The objects of the experiment were to ascertain the following facts: 



1. The effect of a thorough flushing of a basin on the breeding contained 

 therein. 



2. The efficiency of an oil sprayer as compared with that of a sprinkling 

 can in oiling a basin. 



3. The effect of a thorough flushing of a basin on a film of oil on the 

 surface of the water. 



In selecting the catch-basin to experiment on great care was used to get 

 as near an average basin as possible. It was after an examination of about 

 two hundred basins that this particular one was chosen. The conditions 

 were as follows : 



1. The water contained breeding to the extent of three to four larvae to 

 the dip. 



2. There was a moderate amount of rubbish floating in the water. 



3. There were no recent rains to make any unusual conditions. 



4. There was a sufficient pollution of the water to be able to detect any 

 change after the flushing. 



After specimens of breeding were taken from the basin a three-inch hose 

 was connected to a nearby hydrant, and the water allowed to flow from 

 the gutter into the basin, thus obtaining the same conditions that would 

 naturally prevail during a heavy shower. After a continuous flushing of 

 one-half hour's duration the water was allowed to settle for fifteen minutes, 

 giving any breeding still present a chance to come to the surface. The theory 

 was that the agitation in the water did not extend to the lower portion of 

 the basin and that the water lying below the outlet remains comparatively 

 still. This may not be so in a cloud-burst, but is true, I think, in any con- 

 tinuous influx of water, however long the period of flow. During this time 

 the breeding remains at the bottom, only coming to the top when absolutely 

 necessary. 



Further examination showed the presence of breeding still in the basin 

 and to the same extent as before flushing. 



A peculiar feature of the experiment lay in the fact that only larvae were 

 dipped before the flushing operation, while only pupas were taken afterward. 

 Of what significance this fact was, if any at all, I do not know. 



The conclusion reached after this experiment was that showers and mod- 

 erate rains do not flush out the breeding in catch-basins as has been believed 

 heretofore, thus making the operation of oiling unnecessary until a later 

 date. I firmly believe that the oiling of basins should be done periodically, 

 regardless of storms or showers. The interval of time should be determined 

 by the season of the year. Inspection of basins should be made in the be- 



